Apologies for taking this thread down a different turn, and I know we'll never get to something definitive (but it is fun to jaw).
Georg- you are among a pretty select few group of people I can think of that have probably some of the most varied experience with different drivetrain/model combos. Would you be willing to lay them out and give your impressions? I know that I am not alone in considering some drivetrain changes.. here is an example of what I'm looking for and I'll use my experiences as a start. I think it's important to add qualifiers as much as possible to shade the impression. Things like miles on engine (or rebuild), engine health, gearing, tires, weight carried, etc.. it all comes into play. I really wanted to put the weight of my FJ62 (6200lbs now with the winch, fully loaded, all the bumper/armor and roof top tent) into that 13B-T/A440 to see what kind of difference it may have made.
my history:
1974 FJ40 hardtop, stock 2bbl 1F/4spd, mid-high 100k miles, stock running gear, 30" tiers. My first cruiser in '92ish. I knew nothing and it felt like an old truck but it didn't matter because the top came off and I was in college.
1964 FJ40 hardtop, 1F 1bbl/3spd, higher 100k miles, I think it was a "rebuild the top 40k ago" truck. Came with 31" Yoko Super Diggers with probably 40% tread. More FJ40 bliss, but it was a slow, sputtery truck. I went way into the boonies of Oregon alone many times and it always brought me back. Upgraded to 33x9.5 BFG MTs and an 8274 winch, not much difference, harder push to get over passes. 2wd low was fun.
1981 BJ42 hardtop. 3B w/Fairey OD (stuck in OD iirc), otherwise stock. Came with 29" tires, 250k kilometers on the clock. Wow, 450 mile range on a tank. Great gearing combo (stock 4.11 in BJ42s) with the tires and OD. Not fast but capable up a pass. Fairey blew up, so yanked it, rebuilt the t-case, added 33x12.5 MTs. Noticeably more of a dog and passes were more work than the original form. May have had less weight due to pretty terminal body rust.
1982 BJ42 hardtop. All stock, had to be in the 200k+ kilometers. 29" Hankook snow/all terrains. This was an internet deal gone bad and I have it sitting as parts for some distant future drivetrain swap into the '64. Ran fantastic, drove it home to Oregon from Maine in the middle of February. Similar to the '81 in driveability- capable but not outstanding. 19+ mpg. Was loaded with spare parts/tools/extra fluids/duct tape/bailing wire/JB weld. Kind of scary as I found the rear frame rotted. Most the truck is bondo, so not sure if that is heavier or lighter than sheet metal.
80s BJ75 pickup. 3B/H55. 4.11s on 31" BFG ATs. Healthy motor. Heavy mining bed and about 15 leafs on the rear packs. Impressive to see 1 ton of gutted home material loaded without noticeable sag. Empty, it drove capably. Nothing I remember outstanding, felt closer to the BJ42s above. Low mile engine, but they were mine miles.
Mid 80s BJ70 hardtop. 3B/H55. 4.11s and 31s I think. Not sure if I've driven it. Seemed to be close to the BJ75 (same owner). Not sure if engine was as tight as the BJ75.
Nov/Dec 03, '89 FJ-62 stock on 285s. 175k miles, solid compression, untouched drivetrain. 04 saw it on 31" BFG ATs, 33x9.5 (from '64 FJ40) BFG MTs, 33x12.5 BFG MTs ('81 BJ42s), finally 33x10.5 BFG ATs. It started off respectable on 285/31s, but just got worse after lots of miles (240k ish now), and lots more weight- 125lb front bullbar, winch, rear full protection bumper, sliders. 6200 lbs I think was last weigh-in. Complete dog. If it weren't for the 3FE able to rev easily to 4k rpm on occasion, it would be unbearable.
Moab '05, and I get to drive Luke Porter's HJ61 to Poison Spider Mesa, up it a ways and back. 12H-T, H55, very heavy German-outfitted expedition truck with 4 passengers along. 33x16 MTs. Bigger fuel tank, cargo area storage system loaded, roof rack ARB/Kaymar, sliders, winch, body armor. Good tunes. This felt great on the highway with that load. Didn't feel pushed at all, responsive throttle. OME HD with 2 or 3 extra OME long overload leafs at each corner. I think a gear or 2 in the H55 was broken. The expedition tank gave him I think a 1200 mile range on fillup. Maiden Voyage.
'66 FJ454. 45 lpb, bobbed w/heavy steel flat bed. 454 big block, built/balanced, SM465/NP205. Oh my this is different. More power than this old of a truck should have. May have contributed to broken NP205 and rear FF shafts starting to twist a bit.

Have a reman 850cfm q-jet and new matching edelbrock intake waiting for the day it lives again, behind the other projects. Maybe 4.11s on 37s, but really with all the power not sure gearing matters anymore. Pretty confident that engine will continue to roar long after everything else around it shreds apart. It will get shrunk to 35 ATs and get the rear frame re-extened to stock and a nice bed back on, and become a mild-mannered street/snow truck. Nothing to compare to- ok maybe PortFJ62's Merc powered FJ62. He breaks his truck too.
'79 FJ40 soft top. Healthy (smogged) 2F, SM420, 4spd case. 35 MTRs/4.56s. Has some bumper/winch weight. Cruises nicely, can pull a pass ok (in the ballpark of BJ42s feel).
Rowland's 1HZ(with HD-T turbo)FJ60, H55f, 33x10.5s(?). All I can say is he is a bastard, complaining about only able to get up to 85mph up a good mtn pass because ambient temp is 95F. Anyways, I have been around this truck enough times and at length to say this is a pretty awesome combo. It is probably lighter than my FJ62 but it is still pretty loaded with gear in every hidden nook and cranny you may not know exists in a 60. Even a spare jerry can underneath in a stealth holder. My only regret is not driving it. Will hopefully get to that this summer.
FJ62 13B-T/A440. Surprisingly good combo. Would not have believed it. Plenty of spare power. Makes me want to get the one BJ42 back to life and other one's parts transplanted with turbos added. Would still like to load it with 800 or so lbs of sand bags and see how it does.
Other thoughts.. 2FE/H55. I was really going to go this route, but after looking at the costs of a nice rebuild and new transmission, I think there are other more viable alternatives out there for what I have and want.
So I am left to wonder the difference in characteristics of a well-used (250k+ km) 12H-T/H55 (or 1HZ) conversion against a 10- or 1000-mile '02-'04 5.3L vortec / 4L60E conversion on a truck that is +/- 800-1200lbs lighter than the trucks the V8 originally was run in. I explore with more than wheel the FJ62, and care about crossing distances and get over mountain passes than the need for speed or insanely extensive ranges. The diesel has greater range, especially poking along dirt/gravel roads at changing altitudes. It is also heavier, and louder, and simpler. The v8 is lighter, modern (obd-II), oddly simple after reworked wiring harness, and got 15-21mpg in a heavier platform. And has more power. If either gets over a pass easily, which has more power doesn't really matter. Range difference isn't a huge deal as I can work out ways to store more fuel if needed. The idea of smoking Kevin's HZT60 in a race across the Alvord desert has a certain appeal to it, I'll admit.