the battery is at the standard place on the right side of the engine compartment. The car was not repainted, but the engine was in new paint, when i bought it. You think about an insulation by the paint?
The battery is about 9 months old.
As I have forgotten to mention in my first post, the engine barely turns over when hot.
I have no gimmicks built in. Even the radio is still the original one.
I know the mechanic checked the timing (and the vacuum, as he has told me). And he is an hot rodder and drives old US cars every day. I believe, he knows what he is doing.
I could try another ground cable directly from the battery to the engine. It does not cost much and is easy to do. But I will drive the car only as soon as the salt is gone from the streets.