You can spend a lot of time on rules and attempts at enforcement and still not banish suspicions.
Consider instead a simple spec like 540-J's only, confirmed by a simple look. And then, just do a $20 claimer rule. That's $20 and the motor in the claimer's car for the motor in the owner's car. You can only exercise it at the end of the race day after the final main. And you can only claim up. That is, 3rd place can only claim a motor from 1st or 2nd. You can only claim from within your main. A within A, B within B. And you can never claim down. The lowest placed claimer gets priority. $20 is enough to prevent harrasment without being prohibitive.
Forget all the other rules and the hassle and hard feelings of enforcement.
Seattle RC Racers
The world ends when you're dead. Until then, you got more punishment in store.
Stand it like a man, and give some back. --Al Swearengen