One way to move it ever so "slightly" is to put a pry bar between the ring gear and block, and "pry" it about one "tooth". If it moves without massive resistance, you should be okay. Remove all the spark plugs, re-prime the oil system and try the starter again. If it resists, then "pops" free, you have fretting corrosion from the rings to the walls. It will have to come out, be re-honed and new rings.
Best of luck.