braking issue

[camaro427-69]

hey folks

i already changed front and rear brakes. my original setup was disc front and drum back. front has the ssbc quick change 43mm kit and the back has the standard brake kit. i haven´t done any changes in the lines or master cylinder just swapped brakes. the only thing i changed was a vacuum pump connected to a can cause my bbc doesn´t make any vacuum. my problem is that the brakes don´t feel good at all and like i have no assistance. i have to push the pedal really hard to slow the car down. first i thought that the proportioning valve or the valve in the drum brake line is keeping the rears from helping to brake so i´ve put it on my mechanics brake test stand. you should have seen my face when the brakes made better numbers than brand new cars and were perfect balanced front and back. but brake stands and streets are two worlds. could another power booster solve that problem? what´s the difference between the 7" and 9" boosters? i would appreciate more space between valve covers and booster cause i have to use 2 cover gaskets to fit my roller rockers but tall covers won´t fit.

thanks,
pat