I wouldn't mill them that far. All I would do is mill to make sure the surface is flat. Milling to gain compression is futile, as a LOT has to be removed. You can blueprint the deck height, as I am sure it is both too tall and crooked.
A 360 engine can make over 350 HP having 8.5 compression with good parts choices. It's not hard to do and will run all day long on the cheapest pump gas money will buy.
