I would advise against trying anything with S10 or the '88 and late IFS 4x4 systems, unless you're planning a complete frame swap. Much of the suspension systems that go along with those drive axles would take much more work that it's worth to adapt to the early frame. A better choice would be to get a matched set of '73-'87 axles, which can be easily adapted to your existing leaf spring setup. Gearsets are readily available for them, and even with stock gearing, 4.10 and 3.73 are rather common. An additional plus, the later open knuckle front end will have disk brakes and a slightly tighter turning radius. You will want to run at least a 16" wheel with those if you stay with the 3/4 ton, 15" wheels will not clear the calipers. If you go 1/2 ton, stay away from the 3.08 ratio if you plan on any kind of work with the truck, snow plow/off roading. The 3.08 gear is not robust enough to handle it.
I do agree with the 205 swap, it is a drive through type transfer case, eliminating much of the extra friction in the drive system. Look for one from a '70s Dodge, they were mounted as a divorced style 'case, just like the original T221. The NP 203 with a part time conversion would be another viable choice, again, look for the Dodge variant (Boyce equipment used to have them for a reasonable price).
an easier 205 to put in is out of a 70's IHC scout or p/u. with dodge you have to get rid of those oddball yokes on them. if you can even get a r/side drop 205 you can rob the pieces from a l/hand drop 205(ford) and put in the r/side case. the output ratio between a t221 and a 205 are both the same; so if your t221 is in good shape ,run it .
if you cann get a 205 from an ihc make sure thathat you get all of the IHC mounting stuff; it will help with the installation
ron
