I've heard the plugs are numbered according to how the hole in the head was threaded...to allow the gap to face a certain direction.
If this is true remember you can't put the plug from Cyl 2 into Cyl 4 etc. (Unless those two cylinders had the same number stamped onto them)

Efficient drivers do it better.
1003 miles a tank personal record. 74MPG calculated. HCH1 CVT