If it won't budge, it's likely rusted cylinder walls. Keep putting a mixture of atf and diesel in it. Let it set a few days, then try to turn it. You may can remove the flywheel dust cover and use a pry bar to see if it will move any in either direction. Just be mindfull if you try too hard and it does move, you may break some rings.

There is also a sliim chance a bearing (could be rod or main) that is too tight. Has this engine ever been run?

If you can find it in your area, a lot of folks swear by "Kroil". Put some of it down the spark plug holes and let it set a few days.