I very strongly recommend you upgrade to a dual master cylinder even if you leave it as a drum brake car for safeties sake especially if you'll have your family in there with you. I had the single master cylinder fail on my 64 Impala SS and it was scary as chit. The parking brake doesn't do a whole hellava lot at 55 mph and a downshift on a power powerglide doesn't take affect until 30 or under. While you're at it upgrade to power brakes as well both legs will thank you. There are complete kits available a quick internet search will have a bunch. You can go from simple to a full 4 wheel disc conversion.
