How much do you think a 72 coronet with a 318 could tow?

Crazy Dave has it right. There are two factors that need to be taken into account, tongue weight and total loaded trailer weight. Max. tongue weight is going to be limited by the hitch. Short answer is 4000 lbs max tow load. If the load has a tongue weight over 200 lbs, a load equalizing hitch is required.

The photo below is Dave's link. If you're going to be towing often or heavy, strongly suggest a good tranny cooler.