Win71, I have about 4 hours more experience in CAS than you do, so take what I say for what it's worth. But the way I understand it, the only way you'd be able to use those rifles is for long range rifle side matches, and apparently not every CAS event has long range rifle side matches.
As I understand it, the 4 basic lead launchers that you need to compete in CAS are 2 single action revolvers (with about 32 sub classes :lol: ), a pistol caliber rifle or carbine (.32/20, .357, .44/40, .44 Mag, .45 Colt, etc...), and either a side x side shotgun without ejectors or an external hammer pump or lever shotgun. So you're all set with the scattergun, but you'd still need to beg, borrow, or steal a pistol caliber rifle and a couple of six shooters.
If you read over the old threads here, you can pick up a lot of good info. Good luck and shoot straight.