fairly easy...
it's very doable with a little planning.
remember that the cucv body style was available in the one-ton civvy trucks until late 91',and the 4l80 was available with the 6.2 in that year only for this body style.
iv'e done this swap,and it's a really good way to get overdrive besides going manual.i can give a few tips...
first you'll have to decide what x-case your going to use.if you use a 205,which style comes to mind?there are 2 versions,one with the traditional "race track" adaptor and the later"round" adaptor.
the race track adaptor can be macined to fit by getting hold of the out-put housing from a 2-wd 4l80.bring both to a machinist,and the indexing rings can be made to match.for the round style,a factory adaptor exists,but is super rare.iv'e only seen one.
as an option,i believe that an np-208 adaptor can be used with a round case 205,but a couple of holes need some "massaging" to line up.
the trans will have to be dissasembled to get the correct out-put shaft in place.for a 32 spline short 205,with the race-track adaptor,you'll need a 4-wd"short" output with 1/4 inch machined off the spline end.for the round style,use a 4-wd "long" trans output.if measurements say (take lots of these) that there will be a problem,track down a "motorhome" output.these are very long,and splined full length.they can be cut to fit.
while the trans is dissasembled,inspect and repair as req',and replace all the seals and torringtons.use a new torque converter from a 6.5 diesel.the trans bolts to a 6.2 without issue.an np-241 x-case is an option.a passenger drop varient was used on the suberban from 91' to 94' i think.hard to find,but light weight,and fairly rugged.also has a superior low range.
you'll have to use new driveshafts,as the 4l80 is 2 inches longer than the thm-400.a shift linkage will have to be scrounged or built(this took me a while)or use a floor shifter.a crossmember will have to be re-located.the dipstick for the trans is still a good number at gm,but not for long.i used this controller.
WWW.compushift.com
it works well,but is not as adaptable as the tci unit.manual shift is much cheaper,and a viable option.a switch can be rigged for torque lockup,like the switches for the 700r4,with allowances made for the correct voltage to the solinoids in the trans.or get a torque without lockup.cooling lines will have to be made for the trans,and the inspection cover will have to be scrounged.this will be a scrap yard item.
i can't think of anything else off the bat...
