One of the first things you need to do on a car that's set for many years is pull the spark plugs and put a few squirts of oil in the cylinders and let it set for awhile then try turning the engine by hand to see if it free. It is important to clean out the fuel tank of any old fuel rust crud ect. You will probally also need to go through all the brake parts too. I use engine oil for lubing the cylinders but ATF or Marvel Mystery oil works well too. This is in case there is any light surface rust on the cylinder walls above the piston tops these oils will help to lube each cylinders piston rings, clean the upper cylinder walls removing any light rust that might of formed over time setting, most often it won't hurt anything to just try first turning the engine by hand or a socket wrench to find out if it turns fairly easy and if it dose you will be looking good going forward. if the engine is stuck then the lighter oils like penetrating oil, ATF or even Desiel fuel (this method is also used to put an engine in long term storage oldtimers called this Pickling). Any of these oils can be put into the cylinders to soak them and loosen up stuck piston rings by turning engine a little in one direction then back the other way using a socket wrench on the crankshaft center bolt. This can take some time turning it a little at a time then resoaking the cylinders some more but most times if you can move it even a little bit you will be able to get the engine free again over time of a few hours to a few days in the more severe cases but take you time so as to not do any damage to it.
My best guess by your descriptions of the car and its engine being garage stored that it is maybe going to be free so a little engine oil will give the dry cylinders some lube so a couple tea spoons of oil in each should do it. The engines bearings and oil pump are also going to be dry. Examine the existing oil for its viscosity by feel in your fingers compared to fresh oil if it seems okay you can use it to get the engine started and then warm up the engine before you change the old oil and filter if not then you can chage the oil and filter first but know that you will probally need to re change the oil and filter again sooner then normal. Something I would do is to is to run the engine with a flush before changing it do that two to three times to clean out any built up sludge. My favorite for this is to use Justice Brothers engine flush it was a company local and famous in the area I grew up in, I also knew the locale supply rep to. If you decide to change the oil and filter first then when the oil filter is off you can also squirt a bunch of oil into oil filter input port (this goes right down into the oil pump) also fill up the oil filter this will get some lube in the oil pump to prime it and also get lube to the engines bearing a little faster. You will want to turn the engine severial rotations by hand ,first and then you can try using the starter to turn the engine over (pull the coil wire so it can't start) this will help prime and pressurize the oil system it can work very well in getting oil into all the passages. Anther way that's even better is to pull the Distribitor with the engine at TDC on #1 cylinder and use drill to turn the oil pump to pressurize the oil system passages you could also turn the engine a 1/4 turn by hand then pressureize it again turn another 1/4 turn and repeat this until you have turned the engine two full turns this is the method I often use for a new or rebuilt engine before starting it. Best of luck
