pad compound upgrade

not sure, just ordered a Power Stop kit for my daily truck. my 66 Valiant will stop as good as my WRX did. just a 73-up disc master, Wilwood adjustable prop valve, 11.75 front rotors with regular pads and 11" rear drums. I am running more modern 17" tires. hell I know it out brakes the old ladies minivan...LOL any chance that master just isn't enough for your rear disc?