46 A Locked/Seized?

First time with a JD two cylinder. Seller claimed it ran last spring, tried pull starting at sellers location, no start. Got it home set points and timed magneto, pulled to try to start, no go, dropped float bowl, carb all rusted and gunked up. Rebuilt carb but now the motor will not turn AT ALL, drained oil and got 2 pints of water first then slate gray oil and lots of sludge. Pulled crankcase cover off, have yet to drop oil pump but drive coupler "looks" to be in place. Am concerned that all the pull starting was taking place with no oil pressure, man on tractor said it was bouncing up and down on the gauge. It's 6 volt system and after I rebuilt the carb it cranked over maybe 3 revolutions and stopped, now I can't move it at all. So much sludge pickup screen is probably plugged. Is it seized up or could something else be causing the drag on the crank to lock it up on the clutch side? Thanks, sorry so long but wanted to put out as much info as possible, 1946 A, electric start 6 volt, before I took the cover off the crankcase I could take a huge screwdriver in the teeth of the flywheel and leverage against the starter nose and turn the flywheel ever so slightly.

If you haven’t done it already pull the spark plugs out and then try cranking it. You might get lucky and find it’s hydraulic locked with gasoline. Pull the plug wires off the mag before you try cranking it.

I've puled the plugs, same issue. I've put a ATF/oil cocktail into the cylinders through the plug holes thinking if the rings are seized it might loosen it up. I was going to try to put it in gear and "rock it" back and forth but the clutch will not engage. When I push the lever forward or back all I see happening is the crank moves left or right slightly.

I don't know when you did all of this towing trying to start the tractor, but if it was cold you might have broken the oil pump coupling. On these old tractors it is wise to change the oil to get rid of the water before trying to start them.
The next place to look for your problem would be the rod bearings if the problem was no oil pressure.

Yes it was cold, and I've since realized this through research on here. Live and learn, as I mentioned in my OP the drive coupler appears to be in place but I've not had a chance to drop the oil pump yet to verify. I did stick my phone down inside the crankcase and take pictures and it looks to be in place. I'm speculating that since it seems "seized" that the oil pump wasn't working properly. IF it is seized where do I go from here? Can it be freed up short of an overhaul? Thanks

"I've not had a chance to drop the oil pump yet to verify"

Check the coupling from the top, it's NOT just a simple matter to "drop the pump", as an oil line(s) is attached to it, as I recall.