Sending unit size

Spectra makes quality stuff. Mostly Canadian, so much much better than Chinese.

Spectra FG69B is a sending unit with a 3/8" pickup and has a vapor return port. You can neck down the 3/8" to match your factory line. Plug the port if you don't have a return line yet. If you have a starvation problem, you can upsize your hardline as necessary. Running a vapor return will help fight vapor lock. I don't know, but your '72 may have a return line already installed. To get the gauge to read correctly may require use of a meter match or similar device. I don't have any direct knowledge on those, but there are plenty of threads about them here on FABO.

Spectra CR11E is a quality tank. It costs more than the Chinese tanks for good reason. But it's still not crazy expensive.

Shop around for the best price. Rock Auto usually has a good price, but you'll pay shipping. Summit Racing costs a little more, but includes free shipping at $119 (I think). The free shipping threshold has moved around in the past couple of years. Shipping on a tank could be a lot, so where you buy it could significantly affect your total cost.

There are issues with the lock ring and gasket not always fitting. If this happens to you, get the Detroit Muscle Technology (DMT) kit.
Mopar 57-78 Sending Unit to Gas Tank Seal and SS Lock Ring Locking Retainer

If I were in your situation, this is what I would do. Good luck!