Children's Book Involving Witches, Flying Cars, and a Mysterious man who sacrifices himself for the protagonist

I wrote about this on the TVTropes YKTS, but never got any bites. I read it as a little child, mid 1980s or so. It was a book in our house in Ashland, KY. It was a short book, more a short story than anything else. It had sketchy pen and ink drawings in it. The main character was a little boy who somehow makes a pact with a group of witches (I want to say three of them) which granted him three amazing vehicles that were some sort of mishmash in that there was a car that flew, a boat that could drive, etc. This endangers his immortal soul, and he's hiding in long grass when the witches find him. Fortunately, a mysterious old man with a beard, I think also a source of wonders, steps forward and volunteers to be taken instead of the boy, and vanishes in a cloud of sparkling dust along with the vehicles.

Possibly related, or maybe tied to a different book at the same time, I want to say that the witches were very proud of their double-chins, and tried to develop them by pressing their chin to their breastbone repeatedly (when I was a child, I was very proud of being able to do the same). I want to say that there was an illustration of one of the witches doing just that, smiling up through their lashes at the reader.

It's one of those weird things where I read it at face value as a child, but realized later in life that it had a sort of Christ-like overtones, the man sacrificing himself for the sins of the boy.