should I drop the gas tank in my cutlass after?

I think so. Something parked that long would probably be best. If it was not so long I would say just get as much fuel out of there as you can. Add fresh gas to dilute. Replace the fuel filter. Be ready to replace the fuel filter again. Pull all the plugs, squirt some Marvel down there, and crank it by hand. Probably best to do this first to make sure the engine is at least not seized. Clean or replace the plugs. Maybe wires too. Clean the cap and rotor. Maybe just replace them too. Swap out the oil and filter. Drain the radiator and replace with water, can worry about anit-freeze later, and check the rest of the fluid levels. Check the hoses too. Gotta figure they are soft after all this time.

Absolutely, that will probably be the least of your problems but don't let that stop you, Ralph has given you some great advice.

Yes, I would. And replace the fuel pump / rebuild the carburetor.

Back to your lock Q, can you get the key cut code for it? The locksmith can snap you a set in less then a minute.

Yep.
There's sure to be varnish, particles and water condensation in there.