Okay, just finished testing with the fan installed on only one side so I could compare with and without. The prior tests show that I used/heated the left and right fan almost equally when I play, so that's good enough for this next comparison.
WITH the fan kit installed, the right flipper coil range was 79-94 degrees over the course of the game, and it varied up and down a few degrees during the game, not just up.
WITHOUT the fan kit installed, on the same game played, the left flipper coil was 79-123 degrees. It never went down, only up. 123 was where it happened to be when the game ended.
This was about a 7-8 minute game, so it didn't come close to fade level, but these initial results are very promising for being able to keep both coils at a consistent narrow-range performance level from beginning to end with no fade at all once both sides have the flipper coil fan kit installed.
EDIT: Played a bunch more games now with the coil temp probes installed. Some of the games lasting 10-15 minutes and the fan is even better than I expected. At the end of the longest game, the temps were:
Left flipper (no fan) 130F and still rising (never going down)
Right Flipper (fan cooled) 97F to 101F degrees (stayed in this range)
So the fan kit flipper coil was 30 to 33 degrees LESS than the uncooled coil that would have kept rising in temperature! I think we have a winner that will work for all Spike 2 Stern machines to prevent even a small amount of flipper fade on long games. I'll be finalizing the mounting hardware and wire harness design then sending some test kits out, then once those are field tested, these'll be in the Pin Monk store.