Beefing up A500 overdrive

I love it when people talk about power losses in automatic transmissions. You could easily drive one with a Briggs and Stratton single cylinder engine. It wouldn't pull a lot of weight, but the transmission would function fine.
I don't. I've been asking questions about this very subject regarding different transmissions (both auto and stick) and am getting absolutely nowhere. I'd still like to know these things "just because".