Swapping plugs around

Also notice that the newly-revised LMM (912) specifies a higher torque and different gap for the new $$$ spark plugs. I for one will stick with the old-style NGK plugs at the old torque/gap specs.  

I'm not sure why the tightening torque is less on the new plugs, except that the old torque did seem unnecessarily high.  

As for the different gap, the new plugs have a completely different geometry, so that rather makes sense.  But nor can you adjust the (double) gaps on the new plugs.  If they are out of spec, you just have to replace the plug.

My engine came with the new plugs.  They even look expensive.  It now has the "old" ones.  I have not yet noticed any difference in how the engine runs.

I just rotated mine because the front plugs are dark brown and rear are white. I have a little more vibration than normal at start up. So I balanced the prop, balanced the carbs and checked my floats. I thought I would try moving the plugs around. Should go get new ones as these only have around 20 hours on them?

Well, it may help confirm it is not the plug if you swap them and they reverse colors.  A white plug means a potential cooling, timing, or mixture (lean) problem. If both front cylinder plugs are brown, and both rear cylinders have white plugs I’d mentally place ignition timing at the bottom of the probable cause list and look at cooling then mixture. Is your coolant temp gauge plugged into the rear cylinder, and if so, what temps are you seeing at max continuous power?