'Grabby' brakes

I swapped front and rear suspension from a 73 Swinger into my 69 barracuda. Discs,booster, master cylinder, combination valve..... had the rotors turned (thay didn't really need it), i put new seals in the calipers, new braided lines to the calipers, flushed all the hard lines. I used a rebuilt mc/booster from o'reallys. All i did to the rear brakes was clean and inspect, they looked great. The brakes work just fine, but it feels like there's a real fine line between 'lightly hitting the brakes' and the point where they grab and act like like a 'panic stop'. I've gotten used to driving it and it's not horrible, just not as smooth as I'd like it to be. Is there something i should look at or am i just being a picky ***** wanting it to stop like a 2015 car?