Random question for the collective here, but here goes;

Header tank input / outlets. Does it matter about the position of the return pipe? I understand the feed from tank wants to be at the bottom, but does the smaller overflow pipe have to be situated anywhere specific?

To set the scene, I'm rebuilding my Defender 90 300TDi. I've changed the bulkhead to a later one (TD5) which happens to have the header tank mounted to it, whereas the original header was mounted on the O/S/F wheel arch. Originally the pipes both went into the header tank on the base/underneath, but on the newer design the outlet is underneath and the return/overflow is just above the "minimum" mark on the tank. Both tanks remain at the same height across the horizontal axis of the vehicle, in case you were wondering.

So, can I use the later tank or not? Answers on a postcard, please!

No difference.