the GM nv4500 had two different bolt patterns for the bell housing mount and two different bearing retainer diameters. the earlier 4500 (95 and earlier) had the smaller bolt pattern and smaller retainer. High Impact gear has some good info and are pretty knowledgable with these transmissions.

http://www.high-impact.net/transmission_and_gear/nv4500.htm

You should be pretty happy with one of these trannys in your truck, they add to the driveability and give the truck a whole different feel!