provided you are the legal owner of a car, and you modify it to Seven-esque status such as a Pinto, VEGA or Cobra II or something, is there theft involved, ...
Kinda hard for you to steal a car you already own.
if it is your legal title-and such VIN, and parts of the donor car are still present somewhere (axles trans, some panels etc...?)
In Fla the Locost might qualify as a "re-bodied" car. And as such would still be registered as a Pinto etc. with a new body on it.
Since the frame is different etc it might be better if you just use the VIN number as proof where the engine and other big parts came from that you installed in your newly built chassis. With receipts for the metal used in the chassis etc you could present a case that the Locost isn't a "re-bodied" Pinto because the frame was also replaced. i.e. it's a new car built from parts from your legally owned Pinto etc.
Best thing is not try "creative" ways to get around the statutes in your state/province and just research the statutes and do what they require. In Fla you have to bring the car to the DMV for inspection. They might suspect that the Locost chassis/design etc really doesn't look like your original VIN car.
"what if your donor didn't have a VIN to begin with? Before ~1972 VINs wern't required by law. My 69 Europa doesn't have one"
But most likely you DO have a title, so..............?
so if the europa didn't have one how is it registered? do you just make it up with a title? it has no SB # so what gives?
The state had a standard procedure for titling cars before VINs came into being. Once you have a title the car is entered into the system.
For instance, if you were to sell the car you wouldn't bring the VIN number to the title agency. You bring the old title in and they look at the information and go with that.
When I first titled my "new" Henny Killowat EV (made from the chassis of a 1962 non-VIN, never titled Renault Dauphine) the state just issued me the state equivalent to a VIN.
My Locost also has a state issued VIN and it's registered as a "1964 Lotus Replica" (complete with an antique tag).
Part of the paper work I presented to the DMV was the bill of sale for the motorcycle engine used in the car. The bill of sale listed the VIN number of the bike that the engine was from as well as the serial number of the engine etc. So if you are using the engine from your -own- car, just type up an affidavit stating that you are the legal owner of the car (title number xxxxx) and you are using the following parts (engine with s/n, transmission etc) to build the Locost.
I have a page on my website that describes what you need to do in Fla. to get a new VIN/title for a Locost etc. The general procedure is probably similar to other places.