Guess: I'm jmo not seeing anyone that would match up with the Doe's new age/height/weight in terms of someone who'd be very recently missing when this murder occurred. This Doe was murdered in May of 1972, any potential match I've spotted occurs some time before that date range-- so where would the missing person have been in the interim? Most likely scenarios jmo involve
-a runaway (much more likely, jmo)
-and/or some kind of coerced abduction period where the abductor threatened the victim into submission
The Doe had the equivalent of $45 in his pocket. He was perhaps supporting himself on the streets. So I think that Doe himself may have stolen that bike in an act of desperation. The abductor/murderer didn't know about the theft and thought it was the Doe's, left it behind with the murder victim when murderer found a site he viewed as "acceptable."
In the longer-term abduction situation, maybe the victim was getting some allowance from his captor. In such a scenario, the victim again might decide he should steal a bike, it would give him some independence, maybe he could even escape. But he didn't think things through far enough to realize a stolen bike might also draw LE into the scope of things and expose a longer-term abductor. And/or the abductor might have feared that the Doe might well use the bike to take off. My guess is the abductor may have gotten wind of the theft and murdered the Doe.
There are a couple of cases where young MPs disappeared and their bikes were left behind near bodies of water. Nobody knows what happened to these boys to this day, and they've been missing from right around this same timeframe (Richard Huerkamp 1965 Mapleton Minnesota, and James Zapolski 1966 Princeton NJ). And these are only cases I've become personally aware of, there may be more. Obviously, this Daytona Doe is extremely different from these other cases. But there are still some weird parallels there.