I finally tried a couple of experiments that I have been thinking of lately. One, I tried to swap the lower units why I had them off to do the impellers. This did not work, as the guide pins are opposite on the counter rotaion. I was hopeing for a thrust change or better lift or something.
The second was to put a 4 blade, 13 pitch prop on the starbord motor. This was a old prop I had for my 75hp cat. I was able to get on plane with my 115hp. Not sure of my speed, but MUCH faster than the 3 blade, 15p. That brings me to another experiment.
Can I fill the 3 blade props ventilation holes with somthing?

Do you have the round or square holes ?
why would you want t plug them?
the vent holes break the vacume on the back of the prop blades letting the motor turn more rpms and make more HP this inproves acceleration after boat speed picks up over 20 mph or so they have no effect
and yes the lower units are interchangable the upper shift rods have to follow the gear cases and the dowel pins can be rearanged where ever you want them the just press in holes with minimal presure
dang waves are following me home !

YEP... I only turn 5150rpm's now, and 5MPH less. Ok bad experiment :$ Would you think reversing the counter rotation would do anything...good? Also I put the Bob's Machine plates on and don't notice any difference.