Dennis:
If the serial number is
less than 53400, it means that your flash is the older version, and has a trigger voltage that ranges between 200V and 600V - much too high to safely use with cameras that have flash synch circuits that rely on electronic switching components rather than mechanical switching components.
Your F series camera(s) are fully mechanical.
I don't know whether the flash synch circuits in your A series cameras are fully mechanical.
I
think that the flash synch circuit in the T90 is the same as the early EOS cameras, and is therefore electronic, and is therefore subject to being damaged by electronic flashes with high trigger voltages.
You may find the section on trigger circuit voltage in the following link useful (note that there is some discussion therein about the T90, although not in reference to trigger circuit voltages per se):
http://photonotes.org/articles/eos-flash/index2.html
By the way, I definitely wouldn't use that flash with your Mamiya 645 Super, unless you use a safe-synch as well.