In 1980 every fullsize 4x4 GM truck had an NP205 transfer case. Very nice, especially with an Auto, since it's rare. Tranny is probably a TH400. I'm not sure what GVWR the Diesels were available with, but in general a 1/2 ton will have a pair of 10 bolts, the 3/4 ton should have a 14 bolt rear (could be either SF or FF), and a 10 bolt front.
<font color=green>Evan</font color=green>[img]/wwwthreads_images/icons/crazy.gif[/img]
<font color=red>- Contagious Off-Road -