I haven't done this on my car (yet), but I've seen it done by various methods on other cars.

The pedal positioning isn't really the big concern here because when it gets to the master cylinder you still have a pushrod pushing the piston in the master cylinder. So the high or low pivot isn't really an issue. The main issue with the 544 is the odd mounting method of the master cylinder - two bolts thru the side. More modern master cylinders mount with bolts on the end. I think its a matter of making a bracket that goes from the 544's side mounting positions on the body around to the end of the new master cylinder. Sort of a big U shape - with the ends of the U bolting to the car and a mounting for the master cylinder in the bottom of the U. Some careful measuring would have to be done to position the master cylinder at the proper fore-and-aft position for the 544's brake pedal pushrod. Then some creative work with brake lines to hook both fronts up to one circuit, and both rears up to the other. Some more food for thought would be the way drum brake master cylinders need to hold about 5 PSI on the lines when the brakes are released, and disc brakes hold 0. Although if you swap discs onto the front it should be quite easy to find a donor car with front discs and rear drums and a master cylinder with the proper valving for them.

I've also seen swaps done by switching from the low pedal pivots to high by grafting in an entire pedal box from a 122 or 1800. This is a much bigger project - as it also swaps out the clutch linkage. The resulting hydraulic or cable clutch needs the matching bellhousing. Although getting rid of the mechanical linkage on the 544 might not be an entirely bad idea - might make backing up a little smoother... Another BIG issue with this is that the pedal box occupies the spot currently occupied by the heater/ventilation system. Some major creativity would be required to replace/reposition that and regain the fresh air ventilation. Although repositioning that away from the front grill might also not be too bad an idea. I've found that grill fresh air intake is often uncomfortably close to the exhaust pipes of other cars at stoplights.

I'll use the first method when I get around to doing this on my car. Look for a split master cylinder with about the same piston diameter and easy availability (so its cheap) and weld up a sturdy bracket to match it to the car.