Good advice, Over-50. Hall Pantera sells a real safety roll-over valve and adapter for all Panteras, for less than $50. The valve itself is a production Ford-built part. That rivited-on thing at the top of our fuel tank is only a breather; some 1980-up Panteras have a true factory anti-roll-over valve. It consists of 3 separate parts, is tall and is extremely expensive.
I don't like a Christmas-tree of fittings hanging down from the extremely thin steel tank bottom; a few survivors tell of ripping fitting collections out of tanks in a crash, with a resulting fire. So I recommend finding another, safer method of enlarging the fuel feed in Panteras. There are several.
For modified fuel systems, I also recommend using an in-tank fuel pump rather than any external pump. I use a stock Ford TBI pump & regulator with carbs, and a Ford EFI pump for injection. They both fit in an unaltered Pantera tank. In-tank pumps will also be much quieter in operation. With early tanks and EFI, the welded feed line is often used as the fuel-return line.