And if you have disc and disc you still want a dual circuit MC for the added safety. You also want a MC with the required fluid volume/bore that suits your new calipers.
If you swap the brakes front and rear from another vehicle you can't go wrong using the MC from that same vehicle.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
---All pictures---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-