LOL now my mind is racing again.
I'd check out the coffee truck driver. (I've worked places where there were such, even if you don't get your full lunch, you get a donut, chips, back then I think even smokes, etc. You get to know the driver and chit chat). I'd ask RB or other former Dofasco workers or relatives if they bought from a coffee truck.
Coffee truck for a 7-3 shift I'm guessing maybe arrives for lunch (don't know if it would stay a full hour) but say 10:45 arrival for 2 30 min lunch crews, finishes 12, packs up, heard the gossip or confession, is troubled, and heads for the phone 12:18 when no one else is around since they've gone back to work. IMO
Or someone who is totally unconnected at all to Dofasco, who pulled up to the phone booth in his vehicle, made the call. Someone who had been told the story of the murder, by either the murderer or secondhand. if someone is going to make an obviously anonymous call about something so important, wouldn't they want to ensure there was no way to connect themselves to that phonebooth location? i wonder where that phonebooth sits, in relation to just traffic driving by on Ottawa Street? Can you see the phonebooth from the road? Are vehicles allowed to drive up to that phonebooth without going through a gate or something? Would there have been money required for someone to have made that call at that time, or was it like a free call (was it a 911 call?)?