Agree with Larry. That top fitting was for '71-'72 tanks while '73-up did not have that fitting. The late sender is one of the few drop-in parts for a Pantera. You may need to carefully bend the long sender arm a tiny bit to calibrate it to your gauge. Most guys cap the tank fitting or use it as a fuel return for EFI conversions. For that it doesn't matter if it leaks internally.
As for the 50-yr-old non-serviceable charcoal cannister, you can buy a replacement or hook its line to your air cleaner if you need to pass emissions in your area.