[elhigh]

Considering I keep seeing vehicles going down the road with hitch receiver totes on them, I think your extension doesn't really go beyond the limits of what's reasonable. It's about as long a tail as you'll ever see on a passenger vehicle, but only a foot or so longer than a receiver tote, or a power chair carrier.

Blaze orange, or bright arrest-me red, and add secondary lighting. You'll probably have to move the plate, too. This is just me, but I would be inclined to taper the tail in from the sides, as well as from top and bottom.

I remember my experience with an '86 Excel. It pinged almost constantly, unless I poured in a tankful of premium. I hated doing that and as I recall it actually did kill my mileage a little, but it also killed the knock. For the extra $1.25 per tankful, it was worth it. If your ride runs better on the rich stuff, then who am I to argue with that?