that's a good looking old Cougar. I have one that I traded a pair of briar britches for when I was in high school. used to shoot fish with it.
since Milo is the Trad guru here, I don't want to step on his toes, but I'd say you are right on with your brace height estimation, but start low, work your way up. the lowest possible brace height that gives proper arrow flight and least amount of noise is best. bracing a bow too high robs it of cast and places undo stress on the limbs.
Rabbit hunting with bows is big fun with biggle dogs and snow. here's one from last February.