Jeff:
I think these are rare survivals, because the control system on the early years of this style was more prone to problems than the little solid-state control board used on later versions. John combo52 has mentioned this characteristic in the past. Also, I mentioned upthread that your version was installed in the Rodgers House in Fairfield, CT. In her book about the house (The House in My Head, Atheneum, New York, 1967) Dorothy Rodgers has something to say about her JK 29:
"The first time I tried the self-cleaning oven, it didn't; but my second try produced sensational results. (As time passed, we discovered serious cooking problems, and though the manufacturers were as eager as we to solve them, it took a long time.)"
Dorothy's book was a huge best-seller, excerpted (with lots of photos) in House Beautiful, with a clear photo of the JK 29 (in brushed chrome) she was talking about. I've long wondered if that bit of bad press was part of the reason GE redesigned the control system.
Obviously, some of these ovens worked perfectly well - yours is proof positive of that. But getting dinged by a best-selling author whose husband just happened to have co-written The Sound of Music might have been the impetus GE needed to make the control system as bullet-proof as it became later.