A few things to make life easier.
1. Before you install the tank, rig up the sending unit and test the range of your sender to the garage. More than likely the ohms from the sender will be off....and you may need a MeterMatch to get it going
2. Prior to installing the tank....get the filler tube into the big grommet. It's literally impossible to do this while its in the car.
3. Check the seal for the sending unit prior to installing into car. This can be done with a gallon of gas, tilted at an angle....overnight.......slow drips ect.
4. Make sure you have a good thick pad for the top of the tank to protect against vibrations. If the old one looks ok, use it.
5. PM me.....If you need more info.
I just put a new tank in my 1967 R/T, and also noticed the new soldered in vent tube. I also had to bend those rear corner flaps up a bit to clear the tail pipes. Everything is pretty tight there. Aftermarket sender units do not work well with these tanks because of their shape, surrounding the spare tire well. I think the original Chrysler units were calibrated differently, allowing for the odd shape. Mine shows 3/4 tank when I fill it. I only have to drive about 25 miles before it shows 1/2 full. I know my my car gets about 15 miles per Can. gallon, and had 15 gallon tank, so range is 225 miles (these are all Can. measurements). So, at about 200 miles, I am looking for a gas station. I keep a little book in the car and make mileage entry at each full up.