That's a emission "fix" when I was in navy in the 80s Ca. used to do this as part of smog check. Disable vacuum advance to reduce tailpipe emissions, BUTTT decreased gas milage diluted oil thining it and wearing rings all causing more emissions per pound of gasoline, another kneejerk reaction from emission Nazi's that in realality increases emissions by burning more fuel and oil.
That's a cool fury big block, hp manifolds, there are a lot of c body disc brake parts out there everything up to 73 fits don't use smaller car disc setups the spindle too short and too small the drum brakes are powerful just a little grabby and pulls a bit, go to gym lift weights no problem lol good luck.