Hi Dave,
There are three main dwarf cories: Corydoras hastatus, C. pygmaeus and C. habrosus. Back in '07 thru '10 I kept a small school of C. habrosus. As they died-out I never replaced them and ended up trading in the few that were left. I kept them in a 12-gallon Eclipse with galaxy rasboras. They are active little fish that love to swim all over the tank. In my most humble opinion, they are not good for a 55-gallon; they are just too small for such a big tank. Unless you get a large school, all you'll see are a few ¾" fish out and about. Trust me, you'll enjoy them more in a smaller tank.
I've kept and bred rams as well, but in a different tank. With that said, I don't foresee a problem with keeping them together in a 20-long tank, but not anything smaller than that. And of course, as with most cichlids, anything in a tank with a breeding cichlids may not be a happy camper.
David