There is only one connection I can make and it's all speculative.

In Hearts in Atlantis there are a few spots in the story where he describes, from the boy's point of view, the cars the "low men" drive. I think that the driver that disappears in From a Buick 8 is a "low man" and that the 1954 Roadmaster? is a "low man's" car.

That's just the impression that I get. It seems like a lot of the same imagery is used, but I'd have to re-read them both to be certain.