SnakeHerder,

Tell your friend he's looking on the wrong end of the block for the casting number. 1958 and later had side motor mounts ,but they also could be used with the front mounts on a 1955 thru 1957.
You could not use a 57 block in a 1958 or later model.
So You could use a 58 and on block in anything, but a 57 block was only a bolt in for a 55 --56--57.