Oone other option that should be minimal change with redundancy capability (but still the slight possibility of dumping fuel overboard in an emergency situation):
Assuming 6747 valve that you have, it appears that the OFF position flows from the top to bottom output, but not the sides. (Option: Add in series with this the FV-107702 shutoff valve at the seatback or similar shutoff only valve - always open. (emergency fuel off = closed)
Split the fuel feed line before the valve (at the sump?) on each tank to a double throw, double feed electric operated valve pair at the firewall, with the return line ONLY going through this "primary" feed and return fuel system. Now return goes to the feed tank, and switch tanks electrically for normal operation through the weatherhead "flow-thru" position. Adds 1 line in the cockpit.
Auto Valve Emergency fail: switch to L or R with weatherhead, return fuel goes wherever it was going.
It's easy to draw, hard to explain!