Subsequent to This thread I have done some measuring.
And got this:

Prop shaft diagram

So what values do "Flange to end of sleeve" and "Flange to gearbox seal" need to be on here http://www.baileymorris.co.uk/pdfs/kit_car_single_piece_shaft.pdf

Thanks,
Chris

you won't know "Flange to end of sleeve" because it's inside the box, but "Flange to gearbox seal" should be obvious. the seal is in the end of the gearbox. you can see it.

If you give them that figure they should be able to tell you.

Thats all D&F needed for mine.

"Flange to end of sleeve" would only apply if you were replacing an existing shaft.
You need "flange to seal", so 770 plus the length on the splined shaft sticking out from the gearbox seal.

adrian