914/6 alternate rear calipers Options

[Racer]

The rear factory calipers on my 914/6 are giving me some annoyance. In this case, the passenger side rear caliper has developed a slight weap. Its been an issue for the past two years. I've addressed the hard line, soft line and had the caliper re-built, but still, there is a slight leak.

Since 914/6 rear calipers are somewhat difficult to find in working order, I am wondering about an alternative use rear caliper while I sort the issue.

Knowing I would forgo the handbrake/e-brake, would then period (early 911 - 69 911T/912) "m" rear calipers work? I imagine the 912 or early 911T had solid rear rotors vs later vented (wider) rotors and calipers?) What are the piston size differences? How different is the mounting? Would I need a portioning valve installed or modified? Do they work with the stock rear rotor?

The car is otherwise very original, so I am not looking to upgrade everything brakes, just the rear calipers

I know the other answer is "reach out to PMB, they can help you"... and I will.. Just thought I'd ask here too.

TIA