My understanding is the production cars went roller for the following reason. EPA by '74-75 had most cars running catalytic converters. I remember full well by the time these cars had 65-70k miles the cats were plugged even with unleaded gas and folks were cutting them off. It was common practice. The zinc in the oil was blamed, so it was cut back by the mid 80's from around 1200 ppm to about 600 ppm. Car manufacturers went to roller cams due to the lack of zinc and cams going flat. Roller cams are more expensive for the manufacturers and they didn't do it to be kind. They did it, in the end, because the EPA and cats. Now, I'm not saying that roller cams aren't better than flat tappet cams, I'm just stating what I've known to be the reason car companies went roller cams. There were plenty of flat tappet cams going to 200k+ miles prior to the changes.