When using 2 engines together with a common power output is there a
  simple way  to assure that both engines are contributing equal power?
  I can imagine that one or the other could be doing more work even
  though they both are running at the same rpm (obviously). I'm thinking
  of using 2 of the smaller available rotary engines on the
 helicopter,  but my question could apply more broadly to any engine type.

  John McEverett

"is there a simple way  to assure that both engines are contributing equal
power?"

Same problem exists in EVERY multi-cylinder engine.

brian gochnauer

That suggest a simple way to do it is compare EGT's.

Paul Lamar