[kipps]

If it helps at all, my 1987 v20 with a sm465, np208, and a semi-float 14-bolt rear, had a driveshaft that measured 53" between the u-joints, and was 3.5" in diameter. I don't know the length of the slip yoke right off.

Edit: I'm not completely sure about all the measurements in mongo's link. A 1987 4wd sm465 and a 1990's 4wd nv4500 are almost exactly the same length from the block to the t-case. That doesn't appear to be reflected in that link. Unfortunately, I forgot that measurement. I could get it for you though, if it would help. I've got all the parts for a nv4500 sitting around here, and would just need to measure and tally them up.

Also, by the late 80's, GM was beginning the resizing process to make their transmissions more interchangeable. Some of the automatics were being lengthened or shortened by a few inches to simplify truck assembly. I don't know when these changes were taking place, but the gmt400 trucks were more consistent than the squarebody's on transmission length.