Tom,
That’s not abad idea at all to have the right engine for the right track. As far as I know, there’s no rule about running different engines for different tracks but I’m not sure. As far as running 2 TaG classes their is only 1 person I know that does it; Jack Warrington. He runs a Sonik and adds 30 lbs for Masters and takes it off for Senior. There are guys that run 2 different classes like Marc Elliot does. He races TaG Sr. and 125 Pro. Switching weight all the time might get a little old after a few go ’rounds.
If you do decide to look into another package, come see me. I’m selling my Sonik/RBI package since I will be in shifter’s next season. I will be racing at IMI on sunday so stop by and check it out, or you can PM me.