Can someone tell me if a 645 slide and barrel will fit a 4506 frame?

It might fit the early 4506 but look to see if it's cut for the front internal rails on the inside of the dust cover. I don't know offhand if the 645 had them, later 4506s' (4506-1) shared frames with the 10mm and were heavier.

So the 645 slide and barrel definately won't fit a 1006 frame but will possibly fit an early 4506 frame?

You're going tp need someone with a early 4506 to chip in and say if they have the front internal rails, the 645 didn't.