HELP! Spectra Premium fuel tank-filler neck seal

Hello, I bought a spectra premium fuel tank (CR11a)plus sending unit, lock ring for my 1966 Barracuda.
The fuel tank does not ship with a filler neck seal. Nor does spectra make a seal :wack:

Has anybody used these tanks? And what filler neck seal and where did you get it. My project is dead in the water (the old seal, is 48 years old and shows cracking an age)

Any help would be greatly appreciated. The tank is out of the box, nor sure I can return it