as he has a stampede, I am assuming he is not racing at a level where his motor will really matter.
I personally would return the novak motor and go with a 4600 or 5700 motor from castle creations.
As for legality of racing, not sure what class the 7.5R falls into that isnt mod as I believe the spec'd classes right now use 10.5, 13.5, and 17.5 based brushless motors, with 10.5 next year going to mod I believe. So with your current motor he is already in mod designation.
< Durango DEX8, DESC410V2, DEX410V5>
< Team Associated RC10B6D>