I'm a structure man, not an engine man so there's one thing that I don't understand.
AFAIK the coupling of the two engines was trough a mechanical device and my question is: how can two engines coupled by a mechanical device based on gearwheels have a tuning so identical to exactly give the same power at the same RPM? Even a few dozen, minus o plus, RPM of difference between the two engines can put an heavy stress on the couplig device, creating harmonics and consequently vibrations, and overheating. Or there was some particular device to avoid this?