Upgrading my Master Cylinder & Prop Valve - Thoughts On This Combo?

Here's what I have and my plans:
67 Notch, currently with 4 wheel drums. Future plans to upgrade to front discs but not right now.
My master cylinder is weak and I want to replace it right away.

I am thinking of buying a master cylinder for a '73 Dart/Duster setup for front discs, rear drums & manual brakes. I can get one from Rock Auto for about $45 plus shipping.

I am also thinking I will need an adjustable proportioning valve in the rear brake line, planning to buy that from Dr. Diff, most likely.

Will this setup work OK with my current 4 wheel drum setup as well as once I upgrade the fronts to disc brakes? Will I need a different pushrod?
Am I on the right track or totally whacked??? LOL

Want to place the order today in hopes of getting it installed before the Street Machine Nationals this weekend.

Thanks!

-Doug