Good day to install a fuel tank. It was the "hardest" thing I had left to do.
For tips perhaps, I installed Classic Heartbeats grommet. Slid it on the filler neck with dish soap. Installed the tank loosely, with my son's help. Tried dish soap to get the grommet through, failed, probably not the soap. My son kept a blow drier on it while I started it from the inside, finished from the outside, not bad at all. All with a ball-end tool, I swear by them for installing grommets.
NOS cap. And least it was before installed. 71 is a rare cap, I found this in 2017 for $35