I'm at that stage now, despite having loads of finishing off jobs, to consider propshaft and prop adapter. I'm going to be running a ZZR1100 and have standard sierra prop which I was going to mock up so the good people at Dunning and Fairbanks know lengths and things. Only thing is I don't have the adapter yet, but I do have an old sprocket from the bike. Being a tight Yorkshireman I was thinking about manufacturing an adaptor out of the sprocket on my lathe, but then AB Performance do them at £65 so can I be arsed?? But, supposing I can, what diamensions should I be looking at?

Most are 13 splines so check

All the dimensions you need here.
http://www.sprocket-adaptors.co.uk/dimensions.html

Or you could just buy from them!

I bought mine from them....

As above

Thanks guys, that makes more sense. I've got an old gear box main shaft it can mount the sproket I have centred in my lathe it's just a case of being bothered or paying to have a new one.....