Apparently, they made one size delete pulley, based on the smaller a/c pulley that was used into the 94 model year and replaced mid-year with the larger a/c pulley. This is why people with early cars don't have to change belts, but people with later cars do.

The two numbers I mentioned are the length that most aftermarket belt part numbers end with (but not part numbers for GM belts). Sorry, a typo in my notes should have read 635. 635 would mean 63.5 inches long.
GM part number for the 635 belt is 88984193. I'd look for a Gatorback belt 4060635. Cheap from Amazon.

More belt info from Goodyear:

Functional Part Number Gives You The Size Of The Belt

example: 4 06 049 5

1st digit (4) represents a K section Poly V-belt.

2nd and 3rd digit gives the number of ribs (06).

4th, 5th, and 6th digit are the length in inches.

7th digit is length in tenth of an inch.

Part number 4060495 would be a K section Poly-V belt, six ribs wide, with a length of 49 and 5/10 inches.