At least with the Canon 4/5xx EX Speedlites, they can be put in manual mode and fired via PC cord, and you'd have to meter the main flash, adjust power output, and then adjust the power on slaved flashes (It's been a while since I last played with my pair of 580EX flashes so I don't remember all the slave options - not sure if they are electronic/IR only or if they have an optical trigger). So at least in theory, your Canon setup could be used with your non-Canon, non-TTL, non-electronic cameras. That said, although the Speedlites are very compact, they are not cheap, and either eat AA batteries like they're going out of style or require expensive external batteries to power them. What is your interest in subjects to light with these flash units? You might very well be better off getting some dedicated monolights with AC (studio use) or battery power packs (use on location).