Hi Bill: I'm pretty sure this is accurate, at least for these 110 gal. tanks. I'll try to attach a couple of scans that show these attach points under the leading edge of the wings, between the outboard and middle guns. The smaller hole is in front of the larger hole for the respective sized pipes is in a teardrop shaped depression. I was looking through a couple of books, one being Walk Around P-51D by squadron/signal publications, and it show attach points where I have indicated. On the drawing, I have indicated with a yellow circle where you will see two tiny dots that I think represent the attach points for the lines.
I'm certainly no expert on this subject, but from the research I did, and consulting a pilot/owner of a real P-51, this seems to be the case where the lines were attached. It may have varied some when using other tanks, like the teardrop 75 gal or others used in the war, but it looks to me that in every photo or drawing I can find that shows them to some degree, there is an attach point in that area.
Without some handbook showing exactly how this plumbing works, I can only guess as to the true function of these two pipes in the one I used as my source for making the drop tank connections.
davegee