Lynn:  I have a dual Light Speed Ignition set up on my LIV and put the control boxes on the back side of the firewall in front of the rudder pedals--one on each side of the tunnel.  They really don't require much room as they are quite thin.  Now I realize my IV is different than your Super Legacy, but having flown with Light Speed ignitions for about 15 years (on a LongEZ, the Lancair IV is scheduled for a first flight sometime this spring, hopefully...), I think it is worth the effort to find a way to squeeze them in--and outside of the engine compartment is best.  regards, paul