Apologies but I think that the first one might also be "The Fast Lady" with Stanley Baxter and Julie Christie.
No, not "The Fast Lady" either, but thanks for bringing it to my attention. I just watched a fun chase scene on YouTube from "The Fast Lady", and it looks like I need to get the entire film
The first film I mentioned was black & white, all took place in a small village, was very understated (not at all madcap, like "The Fast Lady"), and the majority of the film was made up of the young man building the car, rather than driving it. I don't know if that helps at all.