No, Bangor Punta bought S&W in 1965 and started a period of poorer quality and cost cutting then. After their sale in 1984, things seemed to pick up noticeably. I have a few mid and late 80s guns, and on average they exceed the quality of those guns I own/have owned in the time range 1970 to 1982.
The investment in new tooling and management practices really improved AFTER the P&R decision was made. Also keep in mind, "P&R" were just styling choices, not major engineering changes or features. Especially the pinning, which was more traditional and cosmetic than necessary. Crush fitting was what was holding the barrels in since the 50s, not the pinning.
Your best bet in a model 19 is to individually inspect each one you are considering buying, testing for mechanical condition, b/c gap, endshake, and fit and finish. I would prefer to have a 19, 19-1, 19-2, or 19-5, or 19-6 over the 19-3 or 19-4 ON AVERAGE.
Note the third post in this thread currently running (the one by Hawk). I have to agree with it, things had picked up by the late 70s, the late 60s early 70s seemed to be the nadir of unpredictability in quality:
http://www.thehighroad.org/showthread.php?t=378457