No not screwed in, it's all welded up. I've no idea why they made that filler so tall when clearly the tank was supposed to fit in a very narrow space. Guess I should be glad they didn't make the neck 5 inches tall. Not sure how the protective epoxy would like the heat of cutting and welding, my luck it would be a mess.
After drinking 5 mugs of beer and staring at it, I think I've found a work around, a cut out in the deck above the neck should give it room and allow for access. I can't use a screw in deck plate though so maybe a piece of AL, painted in non skid screwed down over it will give the room needed. This really sucks no mater what after the money spent on the custom tank.