I would buy the kits from NPD. Don't buy NOS. They are always dried out and you'll wind up cutting the square ring when you put the pistons in.
Be sure to check for rust in the piston bores. There is a trick to getting them in. You know how to get a hold of me if you want instruction. I cut a couple seals the last time I rebuild a set. It's very easy to do and you also have to install the boots, which also commonly get rust in them.