The resonance between two engines on a single wng is something that has to be seen to be believed. A mere 12" separation is no hindrance. I recall a friend who put two Fox stunt (glow) .35 engines on a "combat" CL wing. He described the response as like wringing out a hand towel! With the simple, old Fox 35 stunt!

Needless to say, the center section between the two engines MUST be sturdy- or limber enough to prevent linking the two torques...

Some of our 1/2A (up to 1cc/.061 cu in) profile scale multi-engine profiles - Mike Keville rules - models seem to rely more on 'softness' than rigidity.

Whatever works, eh?