If it were mine, I'd buy a nipple that has a nut and o-ring, or make a gasket for it. Anything you glue likely won't hold up to abuse/vibration.
Something like this mounted from the inside would probably work well:
https://www.amazon.com/Sullivan-Products-Aluminum-Fuel-Fitting/dp/B0006O8NTA
I think I have one of those old tanks in a drawer somewhere. Tried fitting it on the side of a savage many years ago, but it was too wide and I didn't feel like doing the mid-tank mod, so I went back to running the 125cc buggy tank.
I do really like the MGT primer bulbs though. Gives me more...