Took me a minute
You DO have 4x disks, right? Why are you worried about residual valves. Disk brakes should not have 'em
But I agree, at this point I'd say an adjustable valve.
I only got my car together for a bit this summer with the 4x disks (Versailles rear, 73/4 Duster front) and it seems fine with NO prop valve, but of course tires, etc, all affects this.