1974 318 alternator

Bob,

You're going to need the square back alternator with two field terminals.

You also need to look at your car to see if it has/had a/c or not...

A/C cars use a double pulley on the alternator and water pump.

Non A/C cars use a single pulley on the alternator and water pump.

You can get away with the opposite one, as it's not enough off to not work, but you will side load your belt and be more prone to them slipping of if you don't match what it should be.

Try contacting Dodge33 brothers, they have a bunch of parts and are only 15 miles north of Battle Creek, MI. Great guys to deal with and very friendly, they will give you a good deal. PM me if you need their phone number.