There are numbers on the back side of a bravo case I have. Are these for shim sizes? Anyone have a clue what they are?

Yes. If the gears have been changed to the newer thick floor style than i.e. If number is 93 it would have been replaced with a 63 as gears are thicker. So basically if you just took apart to reseal and the thrush shims are .063 and case is stamped 93 there's a set of updated gears in there. If the shim you have is .093 and case is stamped 93 original style gears still in there.

That is exactly what they are. Use them as a starting point when you shim them? What are the numbers? It looks like 87. Thin floored gears use a thicker shim, whereas the thick floor gears use a thinner shim. The thick floors are usually in the 64 range, where for comparison I believe the thin floors are in the 90's.

Probably a 97. The older shims came in 91-94-97. The replacements for the thick floored kit come in 51-54-57. But common practice is to check the lash on the gears and set it up properly regardless of the numbers on the case.
These shims are in the bottom of the upper case and in the top cap and provide a surface for the thrust bearings to ride on.

Woops bad info. I just check instruction for gear upgrades it is .040 difference as Mr Gadgets stated.