I am doing steering box conversion and was given a 98 box. I would like to know if there are some numbers or something to let me know I have the right box. Here are some serial numbers that I can see. 26000525, one large Z, 7812145 on cap,322b3 on cap.

The code for the box will be in yellow painted letters, and may be long gone. Look at Jim's page for an explanation of the proper codes:
http://www.chevelles.com/techref/ftecref29.html

I just picked one up and it had a sticker on it with the code. Mine was a wk, a 97 box.