There seems to be a 100-200RPM difference between the port and starboard engines on my buddy's boat. Starboard being the lower of the two. Doesn't really seem to affect driveability. Is this an acceptable range? 496MAG HOs

If the drives and tabs are confirmed to be on as well as the harmonics of the two engines maybe try changing or rewire the tachs from one side to the other. I've seen those be off after some timely trouble shooting.