I'm getting to the end of rebuilding a GSXR 400 SP (GK76), that I purchased in many boxes without a reg plate. A HPI check has shown that the bike has never been registered in the UK. Does anyone know how to go on getting a MOT on the bike and registered?

You can MOT it on the frame number, phone Suzuki GB and ask if they will do you an age related dating certificate, they will probably charge you, then I think you have to send that away to the dvla with more money for the reg documents.
I'm thinking of doing my FZR track bike, I phoned Yamaha UK and got it dated over the phone by a very nice lady as a 1990 bike,( no previous UK reg) she said email photos of engine and frame numbers plus any other relevant details and it would cost me £40 for a Yamaha headed dating cert.

I have a 91 SP frame and v5 if its easier?