[Roadsters] gas filler neck

[Tim]

I want to switch to the filler neck from my 69 part car so I can use one of my locking chrome gas caps (these don't stay on the filler neck from a 70--don't ask me how I know...).

The neck I have has a fair amount of rust on the inside. What, if anything, should I do about the rust? Should I clean it out as best I can and leave it? Or is there something, like POR15, that I could use to treat the inside of the neck? Or will anything I try to treat with eventually end up in the gas tank?

TIA

Tim
Belleville, WI.
'70 SPL AND SRL
Still clueless but always learning