So I am going to go with a fuel cell for my 67 Coronet RT and mount it in the trunk. All stock wiring, for the most part. I am looking at a plastic one with the foam and sending unit. From what I read, I need a sending unit that is 73-10 ohms. Will 70-10 work? that seems to be what is offered in that range. Also, I will need an outlet on the top of the tank for a vent and I am running a return line. Can I or should I run the return line also to the top (different outlet) or to one of the lower sump outlets. I only need one sump outlet for my pump. Thanks!

70-10 won't read right. I went with hyperfuel. Aluminum, 0-90 sender, I just changed my guage. Didn't have to cut trunk floor. I tried 2 different plastic cells, they ended up distorting. Hyperfuel is a little pricey, but has in tank pump, doesn't need foam.

A true fuel cell can be a plastic or aluminum or steel container .., with a rubber liner(bladder) WITH foam inside that bladder to prevent fuel sloshing around.

Any thoughts about a fuel sender for the gas gauge? I would like to keep the factory gauge. Thanks.

Put your original unit back in but your gonna have to recalibrate it to the height of your tank... you will need
to lengthen the float arm.. its easy but might take you a little time.. I did this on mine

I used these guys to update my fuel system. They specialize in what you are doing and their tech is very helpful.

https://www.harmonracingcells.com/

Check out Jaz products. They have fuel cell sending units for most types of gauges.

www.jazproducts.com