The best thing to do, As soon as you think it's done is sell it and start over. At least you won't be spending double on one car . Or Have 2 cars to use your old parts that are not good enough for the #1 to use on the number #2.
I built a whole car #2 with parts that were second to the parts for the car I plan on keeping. Then I sold it. But now I wish I would have kept it until I finished #1.