Re: 1972 Silverline Grand Bahama
I just glued my new transom in, and it took a combined 100 oz of epoxy resin (80 oz) and hardener (20 oz), plus a pound by weight of filler (about another 32 oz by volume). My transom is 74 inches wide by 34 inches tall at the keel. About 15-16 square feet of wood not counting the keyhole.
Haven't filleted or skinned it yet, so that will be another half-gallon or so probably.
West Systems has calculators for various applications that can guide you. My filler calculations were off because I was using US Composites thin laminating resin, and it's a lot thinner than West 105, using more filler to get to the right consistency.
If you're a poly type of guy, there are a bunch of folks here that can calculate materials for that realm.