Chevy V8 to Toyota driveline has been done/adapter plates out there for more than 40 years. If you are dead set on the GM 6 speed you could put in this driveline and connect it to a divorced transfer case and then lengthen/shorten your driveshafts and move your TC shifter back accordingly.........I do not know if the tailshaft can be removed from a T56 to bolt to a TC or not.
Per wikipedia GM L33 5.3L v8 has an aluminum block and was used on 05-07 extended cab pickups. Aluminum block/aluminum head v8 may be close in weight to your 2LT diesel.
A 4.3 v6 would be a much easier fit in the engine bay and produce plenty of power. You would not however have that "sweet v8 sound".
The 4.7L toyota V8 in my 03" tundra is a wonderfully reliable, powerful, sweet running engine. It is also the cleanest looking engine bay under the hood with a total lack of "spaghetti ball mess of wires and hoses". It may be easy to pull a toyota v8 with ECM and transplant, but I've never done it and don't know. If it is in fact not too dependent/intertwined with all the other wiring/electrics in the truck body and it will bolt to your tranny then a toyota v8 would be a sweet swap.
NV4500 5spd would be a good choice for a landcruiser due to much lower 1st gear ratio, and 5th gear is not much lower than the T56. No need for crawler gears in the Tcase with granny low 1st gear. Start off in 2cnd gear for normal driving. NV4500 1st ratio- 5.6 to 6.3:1 5th ratio-.73-1 T56 1st ratio-2.66 to 3.36 5th ratio- .5 to .63-1 . Really no need to short shift through 6 gears with a broad torque high revving v8 in a vehicle you drive at speeds less than 120mph, unless you just enjoy all that gear shifting or want the "cool factor" of having a 6speed.
