If you want power valves then go Cheetah not T-Rex. T-Rex are ok but they are old school. They have heavy pistons and need extra porting to make the same power as a Cheetah. If you have a cool head and reeds of some sort it would be cheaper to go Cub, but if you have the money to spend then power valves are awesome for low end torque. Best thing to do is pick a builder, there are lots of good ones, Fast, K&T, etc etc. Tell them what you want to do with it, dunes, trails, drag race etc. and how much you have to spend, and they will work out whats the best setup for you.