2wd......mmmm i would strongly suggest a vw or benz engine.
sas 4x4, the 4bt makes quite a bit of sense.
with the dub engine or a benz om series in a 2wd greengeeker on this forum has a really good build thread with the dub and there is some om threads as well. with these i would consider adapting a ranger trans or possibly a ford aod/gm 700 r4.....or the electronic variants of such units the 4r70w and 4l60.
with a cummins, the ones on sale in majority right now on fleabay have ford transmissions on them....most are cut outs and they are usually a t series 4 speed with a creeper gear and 1 to 1 final gear. basically a 3 speed manual.
these can be bolted right into a ford fullsize, i see many with complete cooling and fead systems along with the trans for 3500 ish....cant beat that.
the engine weighs 700 pounds, the v8 diesel in my truck weighs the same and in a small 2wd this will not be ideal for traction in less then dry conditions.
there are smaller versions of the cummins, but after watching the development of greengeekers build i would not justify the costs in the general. there are always the exceptions of being in the right place at the right time and getting a smoking deal...but the trade offs in weight distribution and noise vibration and harshness of a 4bt vs a dub engine are on an exponent.
so in a big lifted extended cab 4x4 running larger then stock tires i would lean to a 4bt style, in a low stockish tire 2wd....the smaller engines are ideal by a long shot.
this assumes general use and driving duty of the vehicle. if its just to be a hotrod toy that is used rarely....4bt has the most cost effective power potential....coupled with a nv4500 or zf it could be serious trouble to this chassis.
this coming from a guy that drives a large v8 ext cab ranger daily. and i have owned diesel rabbits on other vehicles as well along with all versions of the first gen trucks from stock powertrains and 2wd/4x4 layouts. to high power powertrain swaps.