Yeah, great find! I think this may be the first time I'm suggesting a repaint, but I'd go for one on that. It's certainly been repainted at least once and will help rid the rust. Good point above from DD about the costs saved upfront helping to offset the cost of a good paint job. All of the details on yours agree with those on my ~83 of a different model where they overlap, so looks like there's general consensus on the ~rough age range, too. One exception: I don't see holes on the drive side dropout for a portacatena. That, I think, could push it toward 84/85ish like Gary suggested above.

...and I think I do spy the diver's helmet cable stop under the chainstay just forward of the clamp-on stop, like SJX426 says. Hopefully the original stop is in good shape and the PO used the clamp-on for reasons unknown. Maybe to look a bit older along with the over-BB cable routing and '74 RD? If it were me I'd slowly replace parts with super record for the correct time period as good deals are found. I'd probably keep at least the retrofriction shift levers installed. Maybe the stem depending. Of course, all of that is assuming the bike fits and you like the ride. So really, I'd go through it first, correct the cable routing, ride, and go from there. Fresh tires could help the ride during decision time.