1966 Disc Brake Conversion Questions
The big question is whether or not you want to keep your 5 on 4" bolt circle wheels. If you do, there are a couple of options. One option would be to find a '66 to '72 A body with front disc brakes and get the spindles, calipers, and rotors from it. These are getting scarce, parts are hard to find, and they tend to be a little pricey. The other option is to get a Scarebird conversion kit. There are kits to convert either 9" drums or 10" drums. What you get in the basic kit is a set of caliper brackets that bolt to your drum spindles and a parts list/instruction sheet. You will need to press the hubs out of your existing drums and bolt the brackets to your spindles. You will need to come up with a pair of Celebrity calipers, Cadillac brake hoses, and a set of Toyota Previa rotors. The rotors need to be redrilled for the 5 on 4" bolt pattern. The Scarebird kit goes for around $150 and has all the special parts you will need to make this work and some pretty good instructions. Either of these brake setups will also require 14" wheels, a proportioning valve, and a dual disc/drum master cylinder.
If you can find a '73-'76 A body with disc brakes in a local yard, grab the upper control arms, spindles, rotors, lower ball joints, and calipers. These will swap directly onto your '66 and give you good braking. You can also get the spindles, calipers, and rotors from an F,M,J body (Aspen, Volare, Diplomat) but these will require the upper control arms from a '73-'76 A body as well as the lower ball joints and brake hoses. Both of these swaps will require 14" wheels, a proportioning valve, a dual master cylinder, and have a 5 on 4.5" bolt circle.
I'm sure I left something out, but it is getting late here in Southern Siberia and this will cover the basics. Good luck with your build.