how far can one turn down a crank?

Seems like you guys are making this way too hard. If the OP is having questions like he is, he needs to turn th crank until it cleans up and go. He don't need to worry about offset grinding and all that.

That said, the Chrysler rod journal is way too big to start. The BBC is plenty big and 2.100 is about good for most conventional BB stroke lengths. When the stroke lengths are short, you can use 2.00 or even 1.88 rod throws and it's much better.