Ok, just a thought.   The 8.4 could have the same depth of the 9.1 provided the area of the depression was a bit larger.  Could pour water into the depression until its full and then do the same for a 9.1 {:>) and compare.  Yes, I don't know of any markings on the counterweights that could be used to sort it out.  Well, I could believe 89-95 would have the same counterweights as those rotors all supposedly weight the same 9.54 lbs regardless of the compression (Humm a bit suspect there), but I would think the heavier 10.4 lbs weights of the 86-88 would require heavier counterweights.
 
Its a bitch when you don't get what you ordered and what's more have little to go by to prove it one way or the other.
 
Me? I'm Waiting for new right-gear leg.  After replacing the clearly bent left gear which had my left wing tip 3" lower than the right, I found that after replacing that gear leg, that the left wing is now 6" higher than the right one.  Taking the right gear leg off and using a straight edge, I found the lower axle area about 3" to the rear of where it should be.  Result of my hard landing back in Feb when I found out that pulling the power all the way to idle made my 76x88 prop act like a very effective airbrake.  The excursion into the ditch when the brakeline blew in June didn't help any I'm certain.
 
But, hope to get it all back together for Shady Bend in October.
 
 
Ed A