Frame number, engine number or whatever. To be able to sell, register, title, license, transfer or whatever you want to do you must have a VIN number in order to be do any of the above to have national inclusion. A VIN number must be generated by the requirements of your state - get a VIN number and you are go to go nationwide. SC had two options for this, homebuilt or reconstructed. My speedster was not a homebuilt (kit car) so that only left reconstructed as an option, which is pretty much undefined. Seems that as little as replacing radiator braces with something other than original would do the trick. (change them back later for the purist). A VIN number will be assigned and you must affix this number to your vehicle where it can be seen, a trophy shop number pop riveted to he fire wall did the trick for me. That is all my VIN inspector looked at, no lights, horn or turning signal were considered. My next of kin, neighbor, car flipper or even the police will never have an ownership problem. VIN number trumps all other numbers. I don't know how the high points people will take this but it is what is - in SC anyway. All that being said I now have a valid license plate.
John