Technically,
NO proportioning should be needed if the front caliper piston size and the rear caliper piston sizes are compatible. Drum/drum systems relied on wheel cylinder sizes to determine proportioning. The same applies with disc/disc systems.
I have a 2.75" single piston caliper up front and the 1.5" piston Dr Diff/Mustang Cobra rear caliper with just a drum brake combination valve. My front skids before the rear but just barely.
View attachment 1715561662 View attachment 1715561663