Through some of my research I've discovered that 499 may have been the only K-37 to have a Flanger Indicator applied to it's smoke box front. The picture in Gunnison shows something that would fit the description. The Service card for 499 also specifies "Priest Flanger Additional" which I believe was the application of this indicator. I've also attached a photo of 486 which has a Flanger Indicator installed as all the K-36's recieved. This is the only photo I have seen of 499 with this applied and it apparently didn't last long. I hope you find this interesting, it was interesting to say the least for me. All the photos are from my personal collection. Thanks.
William
aka drgwk37