Well THAT was easy!

No problem with the Hamamatsu photoreflector chip. Put it on interrupt on RB6 and it ran on the third time I tried it.
It appears that you have to be a little way away from the chip before it sees its reflected light signal. Once I understood that it was no problem getting it to pulse.

Hmmm, I'd planned on that taking longer than it did. I guess I'd better get on with trying to do interrupt-driven serial coms now.