Thanks for the interest all.
The whole idea of this project is to make a bolt-on system that doesn't require any modifications to the engine in the slightest, so in answer to your question Paul, the bottom end is standard.
I will explain a few pointers about what and why I have gone this route:
Firstly these delightful little engines are prone to shearing the crank in half when over revved (a common problem once they have been tuned)
so I decided that I wanted to produce more torque, and not worry about a horsepower increase, this would make the engine far more tractable and user friendly. In turn, I needed to find a turbo that would spin up quickly at lower RPM - the obvious choice is the smallest diesel turbo unit available to me (top secret at the mo!!). Diesel turbos have a different vein angle to petrol turbos, hence the different points of boost.
Secondly, I didn't want to have to muck about putting oil lines in, especially as the twin has only got a centrifugal oil filter, so the plan was always to have its own oil supply, cooler, filter and of course, electric pump all running with a high spec synthetic oil - all fitted on a supporting plate making fitting and removal extremely easy and fast.
Thirdly, because I wasn't aiming for a performance turbo I have opted for a suck-through system. like the old style drag bikes used to use (the carb is before the turbo not after). Another reason for this is I won't have to go to ridiculous lengthes to equalize the pressure in the fuel bowl and create more complications with jetting.
The carb I have chosen is a 650 single cylinder bike carb (huge 40mm).
Because it is sat in front of the turbo, the metering of the fuel is going to be simpler because it will still suck an equal amount of fuel / air mixture. The only negative point, with regards its positioning, is a small amount of fuel de-vapourising as its spun out by the turbo, but this shouldn't cause me any problems as its a relatively low revving engine.
So with all my aims here fairly well complete I hope to have a self-contained turbo unit that can be easily fitted to a standard engine, removed and then back to a stock engine again in a matter of minutes (quite literally).
Thanks once again for your flattering comments, they are much appreciated