>>1987954pads are pretty much universal (some older brake calipers will have slightly narrower slots but can easily/safely be filed open to fit pads)
all nice pads now have toe adjustment so you can angle the pads.
So yeah, reach/ clearance
there's also the recessed vs nutted mounting.
You can get around this. A fork can easily be drilled on the back to accept a recessed nut. I do this a lot.
Drilling the rear is difficult as you need a right angle drill. The easier solution is just to run a modern caliper in the front only (front is 80% of your braking), or, you can run a front recessed brake in the rear (longer), with a traditional nut.