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

[Racer]

Digging around, it would seem the 69 911T and 912's used a solid rear rotor. Starting in 70, they went to a wider (vented) rear rotor. So, the 70+ rear M caliper from a 911 might be too wide. Not sure if they ran spacers to accommodate the wider disc or if the casting was different.

It would seem I would be exchanging one very rare rear caliper for a only slightly less rare rear caliper.

Indeed, I do want to have working 914/6 rear calipers. But given the small production run, if I run into a scenario where the existing rear can't be rebuilt, then I need a back up plan (IMG:style_emoticons/default/wink.gif) Plus, running an alternate rear caliper would give me time to have the originals rebuilt without losing any driving downtime.