ASI H8, I sell the rear tank you want, but I'm not going to get into a discussion about not using two filler necks, I'd use two. The problem with your current idea is you would never know exactly how much gas you have, not to mention all your front gas will not gravity feed to the rear, the tank heights/depths will over-lap. When running both tanks with both sending units (and a double pull-double throw switch, DPDT) you'd always know how much gas you have in either tank, plus you'd be able to run either tank first without bothering the other. Next, if you intend to use your stock dash mounted fuel gauge with the rear tank, you'd have to modify a stock sending unit for use with the deeper tank, and most guys screw up that attempt. You'd be better off using a "240 ohms empty/33 ohms full" aftermarket add-on gauge with a Centroid 240/33 electronic sending unit.
