I just became the proud owner of my great grand fathers 49 New Yorker. It has been parked in the garage for 20 years. Washed weekly ( inside ) and waxed monthly but not started or of course driven. I installed a new battery and the starter wants to turn but the engine will NOT turn over. The oil is full. Is there a remote possibility this car is stuck in gear and that is why it won't turn? Or could it be some sort of fluid lock?

 

I would assume you are pressing in the clutch while attempting to crank the engine, in which case, whether it's stuck in gear or not would be irrelevant. Try removing all the spark plugs and then crank the engine. That will answer your question about "fluid lock". If it still won't crank, see if you can get a socket on the crankshaft pulley nut and try to turn the engine over a little by hand.
More than likely, after sitting for 20 years, the engine is seized up with the pistons frozen to the cylinder walls. If you are lucky, it's just the starter that's seized up.
There are antique auto forums on the web where people deale with theswe problems all the time. I would seek them out.