I did some more research and everything points to an entry level model, circa 1981-1982.
1. The AR derailleurs were introduced in 1981.
2. The Nishiki headbadge had been replaced by decals for 1983 at the latest, according to old ads.
3. I have a database with specs for 65 Nishiki covering a period of 22 years. The closest match is a 1983 Sport entry model for $160.00 US. It had a CrMO frame, AR derailleurs, Maillard hubs (the only model in my data base to have them), 27" rims, stem shifters and Dia-Compe sidepull brakes and 10 speeds. Most entry models evolved form centre-pull to sidepull brakes, implying that the Marina is earlier. However, the presence of 12 speeds on the Marina indicates a step or two up the model line-up. The Maillard hubs seems to be unique to the early '80s, corroborating the era.
If you want to dig deeper, start checking date codes using the information on the Vintage-Trek website. However, check as many components as possible, as some may have been swapped out. The more components you find from the same year, the higher your confidence in the year of manufacture. Please post what you find. If you have problems with the decyphering, or I can help in any other way, please feel free to contact me via private message. Good luck.