If it was early Shimano, I do not belive they ever made a Swiss BB. The way I narrow it down whn I am unsure, is to try threadding an Italian, then Brittish, then french thread BB cup into the adjustable side (all right had thread). The only mystery left is if it is the french that fits(some may fit but are loose, these are not the correct cups). If it is not Brittish (or Swiss), the fixed cup will be right-hand threaded, otherwize, left (and my $$ is on Brittish). Some cups get stuck pretty well, and there are some threads which discuss this.

Rust is a common occurance in the BB of most bikes. Water manages its way in through gas vent holes, the seatpost, condensation, whatever. Unless you have a heap of flakes sitting in it, clean it out, apply some frame rust inhibitor, and move on.