I bought a 65 coronet a few years ago. car had no brakes after a rebuilt 440 installed,then he went through the entire brake system,no brakes-got frustrated- I bought the car,replaced the mopar 484 cam with a more modern style cam. brake problem solved. The 484 cam did not produce enough vacuum for power brakes.(played with carb and timing first though)3 different booster were tried. Other option is to install a stand alone vacuum pump. gm motor homes and some early 80's 4 bangers engines used one.aftermarket pumps are about $250-$300. maybe a manual trans would behave different?