See my earlier post. Methinks this is one reason why a cross-feed alone will not work.
The laws of physics dictate that if the engine sucks through the crossfeed then in theory both tanks will supply the one live engine. I suspect that those same laws of physics will generate a pressure drop across the crossfeed lines leading to a preferential supply from the most direct tank - the one supplying the live engine.
As the fuel level drops the imbalance will grow until the live engine's supply runs out. This will turn into a big headache because once the engine sucks air it will wrap its hand in. Methinks that hauling that inaccessible fuel (200 litres?) around will become tiresome for it can never be part of your reserves.
G.
