1964 Valiant Single to Dual Master Swap Question

Since you already bought the MC, I would run with it. I would tap the holes to mount the dust bellows & stop. If you prefer an alum MC and can return your new MC, see what I did in my 64 Valiant:
Alternative for power brakes , post 28.

Re plumbing. You can buy the 1/4 to 3/16 adapter and 3/16" plug for your distribution block at Autozone (bubble packs). Nice to add an adjustable proportioning valve in the rear circuit.