It's been stated and established that this was a CUSTOM BUILT CAR. However, this process has been reduced to semantics. Unlike the premise of the puzzle, there's no longer a point to it. For me, anyway.
Well, all right, but it's not unusual here on AP for a puzzler to hold out for something that might appear to be nit-picking as we do deal in specifics; I've been the victim of it many times myself when I thought I'd posted the fullest answer possible.
I don't know what other help I could give you, but the expression I was looking for was 'scratch-built'. That implies quite a lot; the parts for it were built up from scratch by the builder, not using bits of fender etc from other cars like many custom jobs. Your second sentence said "I'm guessing that doesn't scratch the itch . ." so the only word there that could possibly fit was "scratch".
But I'm not going to open it up for someone to steal a point they wouldn't really deserve so we'll call it solved. I may not always be so generous though; it's up to the puzzler to determine what he wants and hold out for it if he wants!