anguswilly
+1y
While the 2.6 came in the "pre" B2600"i" which was just a B2600 and it was the same 2.6 Mitsu engine, the big difference here is going to be all the accessories that are different. With this in mind, you are looking at a lot of parts:
Intake and exhaust manifolds
Oil pan and pickup
Crank pulley
The rest of the accessory pulleys
Various brackets (engine mount and accessory)
Flywheel and clutch
Wiring harness
Engine mounts
Rad and fan
Various hoses
Once you figure all that out - you are still stuck with a motor that is infamous for being a POS.
The newer "G6" 2.6 from the 2600i is a better engine (still not fantastic) which makes more power and would be a direct swap if you got everything out of a 2600i, but you'd still need everything and need to convert to EFI
Another thing I would like to point out is that my B2200 cab plus weighs close to 2900lbs and I am not so sure your mighty max weighs 3900lbs - I would think they are about the same weight, maybe you are reading the GVW of the truck?