Hey Jet,
Having the serial number (under the BB shell) might help. My marinoni is from 1995 and the 1st digit is 5. What follow is probably the month and frame size. The best way to know is to email them the serial. In my case they replied very quicly and told to which shop it was sold, with which gruppo it came, who brazed it (probably mr. Marinoni) etc... Very helpful folks.

If the original gruppo is on and is shimano, check the numbers and consult Sheldon Brown's website for dating info.

Paint job seems 80's indeed. Love it too I really like the pantographs on the seatstay caps. And is that a clamp-on front derailleur? Sheesh...