From the photos it looks like the motor could be stuck from bad gas being run thru it before it was shut down.I had this happen on my 48 Plymouth after a long storage.I was young and didn't know any better and fired it up after letting it sit for 3 years.Went back a week later and the motor was rock solid. I pulled the plugs and filled the cylinders with Marvel Mystery Oil and let it sit for a month.When I went back I put a battery to it with the plugs removed and spun it Then she ran fine. Those pistons may not be rusted in place is what I'm getting at so heat and oil may free it
