Hello.
This is my first posting on this site.
I (live in Norway) and have a HJ60 that I am converting to a HJ61 at the moment. First of all I have to say that the soul of the TLC is the diesel engine. All real Cruisers have diesels. I am sorry that you people from the USA have so little experience with them. They are the best and never breaks down.
Anyway, the 2H (4000cc, inline 6) and the 3B (3500cc, inline four) are about the same HP and torque. BUT if you are getting a diesel it is worth noticing that the 3B has the all-important piston skirt cooling. This is a spray of oil that cools the underside of the piston. The 2H does not have this feature that is very important if you are planning on fitting a turbo to it.
The 2H has been known to crack head when turbocharged. This is not due to compression increasing but due to increased heat when burning more fuel. The enigine is strong and handles the compression fine. On a 3B this is no problem the cooling system is the same as the original turbo 3B, the 13B-T engine.
If you really want to do the job right, get the 12H-T (got mine from Germany.) This is the 2H turbo version. Mean setup comparable to V8 conversions but with low-grunt and close to 30 mpg mileage cruising on highway.
And yes: put a snorkle on a diesel and it runs just as well below water as above (ref submarines.)
12H-T pictured below: