Drive Train Axles Bearings problem
1997 Chevy Blazer 6 cyl Four Wheel Drive Automatic 150000 miles

I have a huge problem with my differential. My truck jerked to a complete halt one day-luckily at low speed. I took off the differential cover to reveal many of the teeth on the ring gear had been sheared completely off. The fluid was ruined completely and probably all the bearings-I plan to replace everything. The Question is: it is a 4 door, originally a 4 by 4 (the transfer case does not work) and I want to know what size/type is my differential as the ID tag was not there on the differential. Is there a way to tell from the VIN number? There are many ID numbers in the glove box but that is almost worn away and unreadable. What can I do with only the most basic tools to measure and get a new differential as there are several different differential sizes when I call about parts. Also the pinion shaft bolt has welded to one of the internal gears and I cannot get the pinion shaft bolt out. I spent a full day hammering on it and it only budges a few millimeters. I have given up and will bring it to a differential shop-however they have all told me I need to obtain the replacement differential and I don't know which one it is. Help would be greatly appreciated.