I doubt it based on the time, but could this be Johnnie?http://www.doenetwork.org/hot/hotcase462.html
Even though this man died the same day he was found (3/21/75), he was the only UID I could find that matched Johnnie's description. It's really a long shot, but then again it's still possible. After all, no one ever expected Jaycee Dugard to still be alive after 18 years as a missing person, but she is. Perhaps Johnnie, for reasons unknown, was held captive for almost four years prior to being killed.
It would help if there was a post-mortem photo and/or sketch of the victim. He's not on Namus. Perhaps I should contact the Doe Network to see if I can get more info, possibly the name of the investigator. An actual investigator would likely have much better access to a photo or sketch than the Doe Network staff.
Another possible match was found in Los Angeles on 7/7/77. Again, no pic or sketch and only a vague description. The estimated date of death was up to nine years prior and the estimated age was 16-22; Johnnie went missing in 1971 and was 20. I think of the two, this one is more likely to be him because I really don't think he lived long after he vanished.https://identifyus.org/cases/4440
What do you think?