1964 Valiant Single to Dual Master Swap Question

First step to safety as MoparLeo stated is upgrading. I did the MC swap first. If you're running 13" tires than that must be converted over to 14" when doing a Disc brake swap. Took me a couple years to save up for complete rim, tire swap along with disc brake parts (found everything on this site). But definitely do the MC swap first and it can be used for the disc swap so you're on the right path.