66 Valiant, I want to put in front disk brakes, where do I start and a source for parts

You can always use the stock factory Kelsey Hayes setup. Get it as a complete set off a '66-72 A-body. I'd recommend the '67-72 version for a dual braking system, but the '66 single will work also. Just get it complete with all the front lines (or get new ones), spindles, valve(s), etc. They came stock in both power and manual versions. I like the manual setup personally. You can keep the small bolt pattern, but, depending one which wheels you have, they may or may not fit due to caliper clearance. 13" ones don't work for sure. The 14 X 5 1/2 work. The 14 X 4 1/2 will sometimes work with a spacer. Most aftermarket wheels will work.