I had an engine like this that I found sitting outside. It had been there for about five years.

It was am M-100 6.3 and it would not turn. I removed the plugs, poured in some Marvel Mystery oil and let it sit, upright in the proper v-8 position and not laying on its' side, for about a month.

Then I put a socket on the front bolt, stuck in a cheater bar, and gave it a slight nudge.

And nothing moved.

So I repeated the oil treatment and one month later it nudged a bit. Then I repeated the process.

Finally it moved a little. I removed all the plugs and s-l-o-w-l-y moved the crankshaft bolt. And it turned all the way over with no scraping noises.

I had also removed the valve covers and was watching the valves. If they stick it can cause big problems, so everything has to move in harmony.

And if you do get to to turning over, not running but just turning over, drain out the old oil and put in about five quarts of Rislone. Then turn it over and this will start to flush out all the old oil in the tiny pathways through the engine.

This will take some time, but it is worth doing it right.