Sherman Firefly would solve three problems with one stone - er, tank. It is (mostly) American design (US Happy), served only in Brittish forces (Brits Happy), and would add a second perked tank (need something else to spend perks on, same for bombers, but that is another thread).
Yes, perked I say. That Brit gun was IIRC the first gun to use a Sabot round, and could kill Tigers quite handily.