Hi Slarty, sorry, but I didn't see your post until this morning.
The DVLA rebody rules say that you need the original, unmodified chassis in order to keep the registration number. Most of us took that literally and had the vehicle inspected with the boot outriggers sticking out of the back of the body, but I believe at least one builder sought clarification from DVLA after cutting them off beforehand. The result, as I recall, was that you can't remove anything structural from between the axles, but you can remove or add 'brackets' anywhere that are for body mounting, and outriggers that are outside of the wheelbase can also go.
Just to be sure, if you're at the stage where your body is fitted to the chassis and the engine's in, I'd get it through the registration process asap with them still fitted, then have a ceremonial chopping off once you have the new V5. They do make a very satisfying clang when they hit the ground!
Hope that helps and sorry I missed you at Goodwood, hope you enjoyed it, I certainly did. I even managed to perfect the Jeremy Clarkson 'smug face' look while taking selfies beside the track...
