Remember that your 67' stock firewall does not have room for a booster for your master cylinder, that you need for disc brakes. there are some conversions, but there are always issues. I have not done it, but have heard that replacing the firewall with a late model is the best way to take care of this.
I guess what I am saying, the question you should be asking, (what I asked) do I want this to stop OR do I want to make this the best stopping cruiser.
I found cylinder rebuild kits at rockauto.com. All of my cylinders were original, all frozen, and I rebuilt all of them in a day and a half, for under 100 bucks.
If you want to do it right, and want all the benefits of disk brakes, expect to have the issues with the master and booster fitting. Firewall replace or adapters ( I think there is an issue of hitting the carb unless you went sb chevy) Then all the brake lines, then the new front axle, or swap outers, then the gm conversion in back.........
It is only money.... but how much time you got?