340 break in question

A couple of comments.

[1] I assume the engines were not pre-heated at the factory before they were fired up & checked. And they lasted for tens of thousands of miles...
[2] Roller cams have less friction, post #35. No, actually for two reasons. One, the flat tappet lifter face is convex & the lobe has a taper, side-to-side. This combination allows the lifter to spin, to pirouette like a ballet dancer. Only point contact is made. Over time, as both lobe & lifter face wear, friction would increase. The other friction with a roller cam is the pressure angle. The smaller the base circle, the greater the angle & the greater the levering force exerted on the sides of the lifter bores. On Pontiac V8s that have some of the lifter bores unsupported, & the bores have been known to break from this side force when duration/lift reaches a certain level.