Engine/Tranny Question

I have a big block V8 in a car with an auto transmission. The car has been in storage for a very long time - about 12 years.
After picking it up and starting to work it, I found the engine could
not be manually turned (the electrical system etc is all out for replacement).
I have the plugs removed, and have pour mystery oil into the cylinders in case it is just a matter of the rings being locked to the cylinder walls. No help.
The car has been relocated twice while it was in storage, and since I wasn't there to monitor how it was done myself, I am pretty that it was towed with the tranny in neutral and the driveshaft left connected. I hope.
These tows were probably no more than 5-10 miles max each time.
The question is this. Is it possible that the transmission could be somehow locked up and not allowing the engine to be turned? It is a powerglide. I haven't gotten so far as to yank the whole thing out (which probably is gonna happen sometime in the future to have the engine rebuilt, just not right now cause that is gonna be $2700) but without pulling the heads off and looking, could it be the tranny?
The last time I parked it it was running, but in the meantime I had some "help" from a relative and he smoked the engine compartment harness while trying to "help" me out. His heart was in the right place, but ARRRGGGGHH!
This may be an elementary question, but I know zip about automatic transmissions.
Cheers
Mike
PS I have also learned the value of prepping for long-term storage......
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Towing the car under 50 miles with the transmission in nuetrial will not hurt anything. The reason you don't tow them more then that, is GM automatics have only a front pump. So the seals in the rear of the transmission burn up.
As for the transmission locking the engine, I kind of doubt it. Unless the Torque Conveter rusted up inside, and the front pump is seized. Only then should it lock up the motor. If so, you may have to remove the transmission with the torque converter bolted to the flex plate.
I use PB blaster to free up rings that are rusted/frozen in place. Fill a cylinder, let it sit a few days, fill again. Then slowly start turning the engine over by the crank bolt. Charles
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