[Christ]

A tune-up does wonders for an engine. You might do well to spray clean your engine now, since you're aware of a misfire condition in it's history. You'll want to take a spray bottle full of water, and lightly mist it into the intake with the throttle partially open.

The alternative is just to use some SeaFoam as per the directions on the can, which might appease any fear of water in the engine you have.

As far as the shaved spark plug wire, I've seen/done similar. I got plug wires for the wrong Honda engine before, and just trimmed them up to fit on the engine that I was using. It happens, and if you're good, and use dielectric silicone grease, it doesn't cause a problem. In your case, well... you see.

Unfortunately for your mileage increase, you've also been testing a partial grille block, and one tank just isn't enough to show a marked improvement. Your "improvement" is well within the margin of error, and thus, could be counted as variation. What you'll need for proof is a sustained improvement over an average of tanks.

While I'm not doubting that you got something from doing this, I also want you to know and be prepared for what will undoubtedly be recognized by others.