I don't think it is a big stretch to think the hit on Angelo had something to do with the Luppino/Violi group. The only other current player in town that might have the reason/muscle is the Hell's Angels or Bacchus MC. It makes even more sense if you even remotely accept that Angelo had found religion and retired from crime. He apparently posed no threat, so why kill him? The only logical reason to hit him was for retribution.

Why wait so long? Classic siege warfare. As long as the Musitano's were aligned with the Rizzutos they had some protection. (although that didn't stop Rizzuto's man Pinepinto from being murdered, allegedly by Sal Calautti). So the opposition waited it out, probably well aware/or involved with what was being played out in Montreal. Once the Rizzuto's were weakened, the Musitanos were isolated and vulnerable. Revenge could be taken at leisure. Remember, Musitano's hitman Ken Murdock, claimed he was armed and ready to take out the Luppinos and Violis at a social club but lost his nerve at the last minute. I don't think that is something you forget or let your opponent ever completely walk away from, even if it is 20 years later and they study the bible.