When I did the swap (granted no engine or tranny in there) for the 6.2 diesel and 700-R4, to 350, SM465, NP205, I had to use the front and rear driveshaft out of a 1976 K5, with the same combo. The front had to be shortened to work with the 10 bolt front diff. The rear shaft, besides needing an adapter u-joint, which is very common, fit right in, plenty of travel. I had to drill the frame for the crossmember mounting, the (supposed) 1981 K5 frame I was sold did not have the proper bolt holes for the combo I used. Hydraulic clutch setup out of a newer (86 or so) Chev made it much easier to do the pedals. Still need to cut and weld the tranny tunnel on the truck, to fit the 205's shifter, which is totally different than a 208...my trucks body (1986) did not have a removable transmission tunnel, or I would have swapped it for the correct one like that. Steering Column took awhile to find, (ok I had to make it) but not really a necessity right off the bat.
Personally I'm keeping my eyes out for an NV4500 for the OD, but good luck finding one cheap, ($2000+ used I have seen so far)and you need certain years...not sure which.
Dorian
My K5 and Chev/Olds tech/links page: <A target="_blank" HREF=http://yeagerd.home.mindspring.com/index2.html>http://yeagerd.home.mindspring.com/index2.html</A>