Thanks for the info Dave, looks like this bike's going to take pleanty of sorting!!
It appears it is an R2j that has been raced (not a problem) but then put back as a road bike with different bits and pieces of other models.

I'm going to go to Donnington next weekend for the Jap autojumble (anyone been before? any good for grey imports?) see if I can pick up some parts and hopefully sus out the differences.