Other than the GT classes, and a couple other catch all classes, there is not much allowed in any factory tub classes as far as changing suspension geometry.
Basically they have the rules organized to Limit mods, If your running a camaro,, A-sedan or Touring are the likely slots and they have some pretty straight up limits.. Engine sizes and parts etc.. To be competitive budget 35K in either class. And about a million hours of track time..
Go into GT with a tub car and your getting your lunch money taken..
SCCA racing is won reading the rule book the basic rule is that if its not called out as legal, its not.
NASA has more mods allowed if thats your thing and they are more fun to run with.