Did you put the seal on the fuel pump then slide the unit in?

 

Yes I did, and finally got it on! Thanks to all for the help!

For the next guy fighting that fuel pump and seal -

Before getting it all together and "fighting the good fight", go ahead and fit the seal in the tank without the pump so you can see how it fits. Then, take the seal out and fit it around the fuel pump, but DO NOT put it all the way on. Get it about halfway up so you have some play. Then, put the fule pump (with seal) about halfway into the tank. Fit the seal in the gasket and the rest of the pump will slide right into place. Put the lock ring on with a good twist, insert the fuel line, plug it in and start her up!