Brent,
Latest on the project is that its at my local back street hero whos fabricating the last parts ( primary drive casing, forward pegs and exhaust routing). Struck lucky and found a proper old fashioned british shed engineer who makes top spec drag bikes from the ground up, wheels, frames the lot. Felt very humble wheeling a pressure washer powered harley into his workshop

Should be back in a month or so and I'll post up how i get on with setting up/tuning the CVT and gearing, and all those other little teething problems which are bound to arise.
Gilburton,
I found exactly what i wanted for my project off ebay for sensible money as it was unregistered . I agree if you can find what you want with a V5 then do it and save any potential agro.
As best as i understand it, no emissions test is required for an MOT.
All new builds such as one off custom frames require the dreaded SVA.
To register any other bike will require the SVA if it is less than 10 years old even if its bog standard.
Bikes older than 10 years old are exempt SVA and can be issued age related plates provided you have proof of manufacturer and age.
Projects such as ours can be registered as modified and negate SVA providing certain major components remain as original.
The SVA for diesels contains a particle test but no emmissions test as such. Most properly running engines ought to comfortably meet the requirements as they are not yet as stringent as our petrol friends.
I hope this helps. If you need clarification ring the DVLA as a first point of contact and track down the bloke in charge of SVA . Hes incredibly helpful.
Cheers, Mark