I'm currently in the process of putting P model forks into my M1 zxr frame. To do the swap you need the forks, brakes and lower triples from a P model but can retain your top triple clamp (at least on an L/M, J should be the same).
I've actually got Terry Hay knocking up a hack with some early R1 fork caps and some custom machining to add pre-load adjusters (as opposed to ride-height adjusters) to the P forks too.
At the rear I've got a WP shock with a remote reservoir so can't comment on the stock shock.
Good luck with it, and check out
http://homepage.ntlworld.com/webzxr/zxr750r/for heaps of tech tips and inspiration.