The derailleurs have been swapped. The ARx and AR are early-mid '80s models. This frame appears to have no braze-ons at all, not even a stop for the shifter clamp. Too bad. Getting anything to resist the two derailleur cable pulls with no help while clamped on chrome - uphill battle. If this were mine, I'd consider drilling and tapping a screw where that stop should be. (Probably a pan head that I would neatly file a flat to on the upper side.)

Those derailleurs, while not period, are good derailleurs and to my eye, look like they belong. I'd leave 'em.

Edit: if this bike fits you, keep it! Looks like a sweet ride. Beautiful bike. (And I mean beautiful as in everything looks right. The angles, those lugs, the fork bend ... The stuff you cannot change. Proof that the Japanese knew how to make good bikes a long time ago. Now making them to western standards and appeal and parts; now that was a massive catch-up in the '70s and they didn't always get it right. But that basic frame!)