If that engine is the original engine, It should be the old 207 Stovebolt 6.
I don't know as I'd put ATF in the cylinders (or anywhere in the engine proper, for that matter). I'd stick with a penetrating oil and some motor oil.
You will want to make sure that your top end is freed up as well.
You should be able to use the fan to turn the crankshaft. That engine should (I think) have come with a hand crank.
Good luck!
