I don't know what took me so long to post this, but Saviers Road where the McDonald's at which someone thought the saw Johnnie is only 6 minutes from Cedar Street where the party was held.
I'm really interested in knowing when the witness from McDonald's actually saw the person they believed to be Johnnie. If the info on Namus is correct and Johnnie was last seen alive at 00:30 (12:30am), it seems unlikely that the witness would have encountered Johnnie at the restaurant at that hour as the place would likely have been closed. Also, people back then didn't stop for fast food on the way home from places like they do now; such meals were usually more of a treat.
Anyway, I have a feeling that the sighting is likely an honest case of mistaken identity. If Johnnie was actually at the McDonald's after he disappeared, why was he there and why did he not go home after the party? Even he faked his disappearance and wanted everyone to think he'd been abducted for some reason, why would he then go to a McDonald's that was not only just 6 miles from the party he'd just left, but one where he hung out regularly and would almost certainly have run into people he knew?
Given that Johnnie and Joe are identical twins, isn't it possible that the witness (assuming they didn't see the person he/she thought could have been Johnnie up close) could have actually seen Joe somewhere on Saviers Road when he was on unrelated business and mistook him for Johnnie?
Another important question for the witness would be whether they saw "Johnnie" (that's how I'm going to refer to the man allegedly spotted at the McDonald's, instead of just referring to him as "the man thought to be Johnnie") either enter or exit a car and what type of car was it. I think if we found the car, it would eventually lead us to what happened to Johnnie.
The more I think about this case, the more mysterious and disturbing it seems. A man and his car disappear 7 minutes from home in a heavily-populated residential area and no one knows anything?!? Not buying it.