1973-74 B-body vs 1973-76 A-body spindle

I got the A-body disc spindles from Dr Diff. Anyone have experience with his Stage 2 or Stage 3 kit? Is there a noticeable difference between the 2. I'll be using a 17" wheel on my Barracuda so the 13" rotors would "fill" the wheel better than the 11.75" rotor, But are the 4 piston Wilwood calipers better than the 2 piston Ferd calipers? Barracuda is getting a big block so I need as much braking as I can get.