Have a 1956 Mercury Mont 2 dr hdtp.Have changed intake to a 9425B with a 57 distributor etc,new out of box Holley 390 CFM carb with elec choke;changed to electric wiper motor,vacuum measures 18+.Installed a new m/c& booster from Ir Dave,changed to two brake lines(front and back),replaced a couple bad hoses and some line,changed rod length longer/ shorter ,bled system,checked wheel cylinders and shoe action and everything is working but there is no stopping power above .10mph,like zip.Drum brakes all 4 wheels.The work has been done by a professional mechanic.Is the booster too small for a car this weight?Should I go back to the old Bendix T-V?Is there a later unit that is an easy replacement?Thanks,All help appreciated.