Thanks for the info Garry.
I looked at the hammer mill and told the guy I would take it. I can't recall the name of it but it was an unusual name, not a common farm machinery brand. It was made in Wisconsin though, and was probably 1960's era. It's a standard farm unit with a intake chute, a blower, and a cyclone. I'll have to set a date on a Saturday, lot's of stuff will need to be moved to extract it from the barn. He had another unit as well, a big beast with a big auger on it.
So now I'm on the hunt for a motor to run it, not sure how much power I'll need, but for now it doesn't matter too much so cheap will be the name of the game! I'll go bigger if needed later if plans work out. I've got my eye locally on an old Wisconsin 39ci AGND engine - only 12.5 HP though.