propotioning valve ?

[sst1226]

So I have a question. 69 nova with stock manual disc brake master cylinder 1 1/8" piston and stock proportioning valve, strange 4 piston caliper front brakes up front and getting ready to swap drums out back for 4 piston discs in the rears. Skinnys up front, 14x32s out back.
Will i have to run a proportioning valve to the rear to prevent too much bias/ possibly lock up the rears?
I foot brake the car if that makes any difference, usually leave off the foot brake at 4000rpm.