When you tried to turn it with a breakover bar were all the spark plugs out? If not try it that way before you get crazy and start pulling the motor apart. If that doesn't allow it to turn over then start with the easy things first. Soaking the cylinders, pulling the timing cover, pull intake and heads. Doing each thing then checking for the problem area. If at that point you don't find/cure the problem visit your local banker and call your machine shop. Be prepared for sticker shock when it's done.
