70 swinger gas tank install issues

Thanks guys for all the suggestions. We tried everything again tonight without much luck. Everything is brand new, so I decided to start taking the best measurements I could with my caliper. It's hard to tell exact measurements with 46yr old parts lol. But the filler neck was slightly larger than original and seal was approximately .12 larger where it meets the tank. We decided to use a fine file all the way around the groove that sits in the tank edge several times until we could get the filler neck to start pushing in. Eventually we were able to force the filler neck in the seal. I really didn't want to mess with the seal but I'm confident it was still hard to push in and should seal without any issues. The seal was OER brand I beleive it was from year one, I guess that's the way it goes working with aftermarket parts. Thanks again for the suggestions!
Mark