Replacing single reservoir M/C with dual reservoir on four wheel drum system

I recently bought 13" tires for my '63 Valiant wagon; more recently, I've been thinking about disc brakes for the front. Argh! They are only available for 14" and 15" wheels and tires.

Plan B is to buy new drums and shoes, and a dual master cylinder (for manual braking). Has anyone done this - and can a recommendation be made?

Dan