The 3mm Allen bolt (the middle one)that holds the pads in place on my MPH caliper has disappeared.

I know the original MPH was based on the C2, but the design changed for later MPH calipers, like the one I've got.

Finding a replacement bolt is proving difficult, so would I be able to use a C2 split pin instead?

Even assuming it fits as a bodge, would I be in danger of my pads flying out halfway down a hill?

I'd happily use a split pin.

C2 pads have two holes, held in by two split pins.
MPH pads have one hole.
Can use MPH pad in C2 caliper, but not the other way round.

Anyway, I have a pin in my MPH caliper (which works with a C2-Pro lever) and it's fine.