340 dyno chart thoughts

In the old days engines came with cast-iron rings. These are pretty hard. So they had to wear a while to conform to the cylinder walls and maximize the ring seal. This usually took a few hundred miles.At the end of this period, the engine made a bit more idle torque, and the rpm might rise some 50 or so rpm. Power would be up too on account of the better ring seal.
Modern engines may have moly 2nd rings in them. And modern boring equipment makes a rounder,straighter, smoother cylinder wall. When the cylinder walls are finished with regards to these moly rings, break-in can be extremely short.Shorter than the cam break-in period.