Owning a classic shop and having installed many tanks, we haven't had a lot of problems with leaks. if possible use the original ring, if not just pay close attention while tightening the ring down for any distortion if the ring.
If you really wasn to be 100% sure, cap off the openings and pressurize the tank with 5-10 psi of air (NO MORE). Spray any suspected areas with soapy water and it will bubble if leaking beer
NOTE: if using a repop sending unit you'll likely be removing it for adjustment as I have yet to find a source for accurate
Sending Units. Maybe some one else will chime in whistling
A method I have used on empty tanks out of the car
1. install the S/U. measure the resistance of the S/U should be ~ 75-80 ohms. Flip the tank over and measure it again, Should read ~ 10 ohms
2. Another solution is
TANKS METER MATCH

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