Brake force not properly distributed!

Hello, can someone tell me how I can optimally distribute the braking force at my 1966 Chevy impala? My Chevy had tuv yesterday, without problems However, my mechanic told me that the rear brakes pack more strongly than the front ones. History: the Chevy had all around drum brakes. the rear ones were always perfect but the front ones always pulled alternately to the left and right… …so I got a disc brake kit. so the front drum brakes were so for disc brakes with brake booster. did also work wonderfully… but I noticed that when braking the rear ones immediately block and at the front little comes. that’s not good… in the engine room, under the brake booster, the brake lines go into a magnesium part, I believe that is a valve…. is there the possibility to increase the braking performance of the front disc brakes, or to distribute better?? I WHEN NIMMA CONTINUE… I would like to ask for Your help. thanx! Chevy guy