James,

I have the Viking installed with a 3.25 gal rectangular header tank mounted in the access bay behind the seats.  I have the std 10 gal tanks in the wings with the VDO level sensors installed, but I have a Belite Fuel Probe installed in the bottom of the header tank.  The header tank is vented thru each wing tank.  I've currently installed a Belite single display gauge connected to the probe. 

Nobody out there has been able to tell me definitively if the high pressure unused fuel return line (43 psi)  will have an effect on the probe.  We've reasoned out that if the return line is distant from the probe location and if all tanks are vented, there should be no problems.  However, if it does not work out my plan is to replace the single display Belite probe level gauge with a single Belite dual tanks display utilizing the VDO level senders.  This will not register the 3.25 gal in the header tank ... I guess that will become my reserve.

I hope to get my beast (N701LT) moved to a local boatyard to complete the rigging of the wings; calibrate the fuel probe; and fire up the Viking 110 next month.