I was in the same situation about 6 months ago. I had a gmc 248 that was stuck. I filled each cylinder with a 50/50 mix of kero and marvel mystery oil, let it sit for a month, then I used a screwdriver on the flywheel to turn it back and fouth. Unfortunately I couldn't get it to run do to low compression so I dismantled it. My low comp. was caused by broken piston rings in every cylinder. Good luck and P.S. if it runs I would think about inspecting everything so no further damage happens.
