GMS wheels don't only fit on GMS hubs.

The GMS 1/10 scale hub is the same as you would find on an oval pan car only drilled/tapped for a crown gear on the drive side.

1/12 scale hubs have been used by GMS, Dragmaster, Lockmann, etc. The GMS Tires (actually TM) and Lockmann 1/12 tires will fit.

Car balance is easy. Move weight to the back unless it starts to wheelstand. Too much weight in the front will cause an overstuck/twitchy sensation.