555 is a decent motor and useful for upgrading Williams brass, many of which came with 550 motors. You could list them but I think what John was saying its the mounting adapter thats needed for most any motor upgrade.
What the O gauge world seems to be looking for is a bolt on replacement for the Lionel Pullmor. Right now the only option today is a 385 can with a Frank Timko mount. The hot setup would be an easy way to mount a 555 instead but so far no one has come up with and solution to do this.
Pete
