I'm no lawyer but I think if you altered the ghosts and pacmen to different original characters and did some creative titling that you could possibly do a release and avoid any unpleasantness. Especially if it was released as freeware. Given that you had no access to NAMCO code and did all this from scratch as long there aren't ghosts and pacmen I really don't see how they'd have a leg to stand on.
For your purposes there is no reason to go through that work to change all that and I think at this point your wise to be keeping this to yourself but the gameplay really is coming along so well that it is a shame no to put your work out there in some fashion. I am sure most folks here would like playing your version even if it was monkeys chasing 4 sentient bananas or something. Then you could call it Banana-Royale. Just an idea. Hell, have a contest to redesign the characters for a public release. Winner gets his face/avatar as a piece of bonus fruit or something.
Just something to think about!