Seeing as I can't find a set of quarters for a '73-'74 Road Runner, I am wondering what the difference is between those and a '71-'72?

If there is not much difference, I would be open to getting a new set for a '72 and cutting out what's different and adding that from the '73 assuming the '73 parts are still OK. I mostly need wheel arches and lower quarter replaced, but would prefer working with a full quarter.

Same goes for the trunk drop downs.

The wheel arches and lower 1/4's are what's different between 71/2 and 73/4. The body line is much more sharp and pronounced around the wheel arches and the 71/2's have an extra body line about 6" up from the bottom of the car, a body line that was smoothed out for 73/4.

Well, that kills that idea. That's parts of the quarter that are bad on this car.

I have one of each in the garage and will second the statement that they are completely different, different enough that you may be better off starting with a slab from a old hood or something.