I just did this to my 109" pickup. You'll need to cut out the lower rounded portion of the middle crossmember and weld a flat plate over it (it hangs down enough that it would hit the tank). That's the main difference. On the station wagons, that middle crossmember is square with no PTO hole. Land Rover assumed that you'd rather have the PTO functionality on the pickups than on the SW's. Also, you will need to trim off about an 1" on either side of the "wings" (small steel tabs that extend inward from the spring hanger mounts), and cut off one exhaust hanger mount that's in the way. Other than that, you're good. The bolt holes for the tank are the same and mine were already all there.
Of course, there is the aforementioned rear bed modification for the filler.
61 II 109" Pickup (Restomod, 350 small block, TR4050)
66 IIA 88" Station Wagon (sold)
66 IIA 109" Pickup (Restomod, 5MGE, R380)
67 IIA 109" NADA Wagon (sold)
88, 2.5TD 110 RHD non-hicap pickup
-I used to know everything there was to know about Land Rovers; then I joined the RN Bulletin Board.