It depends on many things. To be honest with you, if the car has not been left outside in high moisture areas, I would most likely yank the coil wire, and or pull the main power wire out of the HEI distributor then spin the engine over a dozen times or so. Then reconnect the distributor, hold the pedal to the floor (because it will have extra gas in it from spinning it), then try to fire it off.
Your gas is going to be pretty ugly, and it may not run all that great until you can get a fresh tank in there.
Now, a car that has been outside, in moist areas needs a little more care. Since some of the valves are left in an open position when the motor stops, moisture can go through the intake or exhaust and start rusting up the inside of the engine, as well as moisture in the block slowly causing the exposed metal surface (cam lobes and lifters in particular) to get a nice coat of rust. So, in that case you should pull all the spark plugs, drain the oil. Replace the oil, and spray some liquid wrench, WD 40 etc. in the cylinders, then spin the engine over with the plugs out and relubricate the best you can. Then pop the plugs back in, hook everything up, cross your fingers and fire it up.
18 months is really not all that bad, so I would not sweat too many details here. You may end up with some nasty rear main, trans, and front seal oil leaks however because they will dry up and crack when left alone as little as 12 months.
Good luck, and welcome to CAC.
Tell us more about your car, and why it has been abandoned for over a year.
