I haven't done the conversion but 3 days ago I ordered this power brake conversion kit from Leed Brakes, though I bought mine using their ebay store ($899):
https://leedbrakes.com/i-23438943-power-disc-brake-conversion-1971-73-mustang-4piston.html
I asked a few questions before I ordered it:
Calipers and pads are same as 65 - 67 Mustangs, so no problems if future replacements needed.
Booster used is a 70 to 73 Mustang booster and master cylinder. Leed say it will clear the clutch linkages on a manual car (mines a manual).
The brake pedal does need modification though, a half inch hole needs to be drilled in the pedal and the a new connecting pin installed 2 inches below the original. Pin is supplied with the kit and is held on with a nut. Leed say a standard power brake pedal will work perfectly if one can be obtained second hand and you can't be bothered with drilling the original.
Have just asked Leed if rotors are specially made for the kit or standard, awaiting their response.
There's an installation instruction pdf for download at the bottom of the linked webpage to read so you can see what you're getting into (plus a short video). Noting that the instructions say that holes need to be drilled into the firewall to fit the booster, pretty sure this is not required as the holes are already there.
I'm not sure when I'll be able to book it in for installation, probably sometime in the next month or so, and will report back then on my thoughts. Really looking forward to getting rid of the drums for good!