I just got what Dave was saying. The drawing shows the outlet fitting 1-1/2" from each of two edges and the inlet fitting 4-1/2" and 6" from the edges. The distance from the center of one fitting to the center of the other is therefore

sqrt( (4.5 - 1.5)^2 + (6 - 1.5)^2 ) or 5.4 inches
This is a bit close. If the inlet fitting is moved from 4-1/2" to 7-1/2" from the edge, the distance is
sqrt( (7.5 - 1.5)^2 + (6 - 1.5)^2 ) or 7.5 inches
This gives considerably more room to work and can accomodate elbows with longer barbs.

Related stuff

SailNet carries a number of things that might be needed for installing your tank. This list is not meant to imply a recommendation. Perhaps after I install my tank I can offer better advice, but this list is just to help you find the parts. Feedback on the suitability of these parts is welcome, preferably to the mailing list.