OK there's been some exciting developments. I finally got the year of the first bike! I dropped a line to Marinoni and they helped me find the serial number and determine the year and original specs.
The Marinoni Quebec is called Marinoni Fleur de Lys and mine dates from 1979. It seems to be a higher-end model, judging by the components and the original price (2000$+ in today standards). All components seem to be original except for the wheels, which were upgraded somewhere along the way.
I'll have to wait to know all the details about the second bike, as the serial number seems to be on the fork and I don't want to unmount it from the headset for now.