Hi Scott,
If you look in Section 24, Table 24-1, of the
G3X Touch install manual it will outline the sensor types compatible with the GEA 24 when interfaced with the G3X system. It is found here
http://static.garmin.com/pumac/190-01115-01_AG.pdf
For your fuel quantity specific question, any resistive or capacitive type fuel senders as supplied by Vans (or other supplier) will work well with the G3X system.
Best Regards,
Brad