@kerak

I’ve no personal experience with the CPP kit, but I’d suggest contacting CPP and seeing what they say about it.  You have to consider that these cars weigh between 5 and 6,000 pounds so they aren’t going to stop on a dime.   If it’s really not stopping well there’s obviously a problem somewhere that needs to be sorted out.

Are you sure both the front and rear brakes are functioning properly?  Did you install a new dual master cylinder, power booster, and proportioning valve with your kit?

Good luck!