I have a feeling that an aux tank, sitting on the back rack, high above the top of the main tank, in this manner will overfill the main if you mess with the venting on the main. You will end up puking gas out the overflow.....not good. (liquids seek an even level...)
My pal Roger ran an aux tank on the C14 in the Ironbutt 2009, and I believe he had an inline shutoff for this exact reason, as he was puking fuel out the overflow because he messed with the vents. I'll ask him what his final solution was, and get back to you.
Adding a pump to force fuel from B to A will exascerbate an alredy potential problem....
I beleive Davo Jones also had this exact same dilemma, and used a manual shutoff, and only filled the main from the reserve when the level was low on the main, not running a closed system with both feeding constantly.
if you tied the main tanks vent, directly to the aux tanks vent, you would get a constant flow, but if you by chance opened the main tanks lid, it would erupt the full contents from the aux tank out of the main tanks cap in seconds.
so with the reserve sitting up there where it is, resign to the fact it can only be used to refill the main, by opening a shutoff valve with the main cap open. The main cap was never designed to resist the overpressure of pumping fuel into it above atmospheric pressure, with a head height above the filler neck. A bit more thought prior to the expense laid out would have made this all clear, sorry to be the bearer of sad tidings.