I bought a 49 Chevy PU one time, for it's cab. Wanted it for our 50. The engine in the 49 was siezed terrible. I couldn't resist
I put many many flavors of oil in the cyls, and let it sit a day or 2, blow it out with air and put a different flavor. Repeat, rinse with solvent, etc. Did this over about a 2 week period. And I gradually got it broke loose. A teeny bit at a time it would turn further and further back and forth. Until finally it would go through.
Then I pulled the cab off, and forgot about it a month or 2.
And one day I was bored or got a wild hair, and decided I would make that engine run
Like I say, it would spin. But there wasn't anybody home.
That engine had 30# on 1 cylinder and 0# on 5 cylinders.
I tried more oils of various flavours to no avail, the rings never freed. And I got to thinkin. What's to be lost? Nuthin.
So I put about all the oil I could get in each cylinder. Got all my ignition and carb just perfect. Put 12 volts to the 6 volt starter. Gave her a good heavy overdose of ether.... hit the starter and oh that was a pissed off motor for 20 or 30 frightening seconds cuz I just kept laying the ether to it...and then blam, that thing was runnin.

AND it ran sweet(on gasoline) no knocks or misses BUT....
God that engine smoked. We laughed until we about cried. Named it Smokey

. Ok, so I set me a bucket up on the frame and hoist my carcass up there and sit at the wheel and throw her in gear and dump the clutch.... and Smokey smoked 'em. Oh man it was funny. The tires were 30+ years dry rotted and heaving chunks. You couldn't tell which end was making the most smoke. That was a good time.