I had a ringless 400 billion mile 273 once (ran great and didn't smoke unless you fed it the gas too rigorously, if you did it would lay down a smokescreen that would make 007 proud, replete with solid oil droplets) in which I prided myself in running (burning) Empire brand SAE 40 (the cheapest stuff you could get at the A&P - came out of the bottle black!
). Every two weeks added two cans of STP, I even re-bottled used motor oil from my other cars to run thru that one. Oh, the many joys of driving junk! 
I never killed that motor and sold it after years of use when I put the 440 dual-quad motor in the Belvedere. I loved that motor so much, I found it and bought it back 10 years later, now I can go out in my yard and look at it and turn up a cold one while I reminisce about the good ole days...