Scarebird sells a kit for adding disk brakes to the rear:
https://scarebird.com/index.php?rout...&product_id=80 You buy their brackets, and then use commonly available rotors and calipers you can get from the local parts house.
edit: You better check with them to make sure on the application - the header says the kit works for up to 1970 cars, but the text says only up to 1964. Scarebird is a member here, he may see this post and elaborate.