i have just (aquired a chassis) can i just make my own chassis no up, or is there a set formula to use, ie donor car nomber.thanks in advance,johnq

Yes, there is a set formula to use. It's defined in BS ISO 3799, BS ISO 3780 etc. but to shortcut the need to read the standards get a number from your local DVLA office. Tell them you are making a kit and they will (should!) help you out.