Converting to front disks

Putting any proportioning valve in the system makes the peddle feel harder.
If you have the original 10 x 1 3/4 rear brakes, keep them. This reduces the rear bias significantly. I drive mine without as much adjustment in the shoes so the pedal travels more thus giving more front bias.
Big bolt pattern on the rear can be done easily by using DrDiff axles and six cylinder B body drum. (Retains A body Backing plate) Drums are hard to find but soon I will do a write up to explain other drums that can be used.

Finally on the fronts read the multitude of comments on this forum with plenty of great insight from everyone who has done this. My personal preference is to use the SSBC kit. They still offer the dual pattern 5 on 4 and 5 on 4.5 rotor and uses the Kelsey Hayes caliper. The whole kit is based on the mustang disc system(KH calipers and Mustang rotor) so you can keep the SBP up front or change out later by swapping out your lug studs. Only catch is that eventually SSBC won’t provide dual pattern rotors for replacements. (I’m working on fixing that as well.)