Re: drum brakes on 65 chevelle
I would spend the money to upgrade to front discs (power or manual your choice) and a new dual reservoir master cylinder. That's what I did with my 65. The drum brakes were fine when I got the car but that old single reservoir master cylinder is a bit scary because you could lose all your brakes at once.
Upgrading your brakes is the first and best modification you can do to your car with both improved safety and performance in mind. Money well spent IMO.
My 64 El Camino has front discs and rear drums with no power booster, works fine.