Is there anything I should be concerned with? I’ve got front disc kit from Summit. Im using a master cylinder and proportioning valve from a 1980 Regal.
If it will all bolt up, that should be half the battle. Is the Summit kit basically a stock replacement or did you go with bigger brakes?
Power brakes on the 66? The master cylinder needs to be matched to the booster and/or the pedal as far as pushrod lengths. And you'll need an adapter for the 3/16" brake line to the rear, 67-up was 1/4". You'll have to do some custom plumbing unless you want to buy the conversion parts.
Manual brakes. It had a dual reservoir of unknown origin. I will check the pushrod length. How much free travel should it have?