Tim I was thinking the way Combat described it. The gain I was envisioning would be when the reed on engine #1 closes and so sends a negative pulse wave back up the intake away from the crankcase. This pulse would travel back up toward the carb and would tend to branch so that some of the charge would want to go back out the carb and some would branch and go into the intake tube/runner of engine #2. This pulse would coincide with the opening of the reed on engine #2, so that you would get the usual amount of charge that would get sucked into engine #2 as though it were by itself PLUS a little bit of extra charge that would be in effect 'supercharged' into #2 by the pulse from #1.

I bet this could be made even better with a V block like Combat stated since 2 small reeds would be lighter than 1 big one. I forget the formula but as you decrease the size of something the weight/mass decreases faster than it's volume/displacement/area. I think the mass decreases by a factor of 4 whereas the surface area decreases by a factor of 2, or something like that. Anyways, this relation is part of the reason for the trend to multivalve engines. You can make 4 small valves breathe the same volume of air as 2 regular valves with the benefit being that the 4 smaller valves will have less reciprocating mass (and so inertia) than 2 regular ones.