How can you tell the gear ratio in a bravo 1?

It is usually stamped in the decal on the side of the drive. Also, if the gear set is out, you can count the teeth on the upper/lower and pinion and then match it up I think

Its stamped underneath the MerCruiser sticker, on the port side of the upper housing. Stamped into the aluminum. It can also simply be printed on the sticker in the same location. Hope this helps.

Probably 99% of merc black engine boats had 1.5 ratio drives.