You may be overthinking this vastly. All in the world that the centerline of a lobe "IS", is, it's the true peak of the center of the lobe, the point at which the lifter is teetering at the peak, has just come "up" and is getting "ready" to go back down
YOU CAN NOT measure it at that point, for the same reason that you cannot measure TDC actually "at" TDC.......in the case of the piston, the action of the crank coming "up and "over" center makes the piston slow way down, actually stop (of course) for a split instant and head "back down" ATC
So whether a piston and measuring TDC, or a cam lobe and measuring centerline, you SPLIT the measurement so that it's equal on both sides of the peak.
It does not REALLY matter what this IS so long as you are consistent, and so long as you give it "enough" movement to maintain accuracy, without using so much movement that you actually introduce errors.
All in the world that you are doing...........
Measure maximum lift by watching the indicator, and NOT what that is.
Back up the engine, WAY before "the event" so as to approach again with "slop" taken up in the chain, and bring the lifter up to .050" BEFORE your max reading.
NOTE the reading on the degree wheel.
Now go "up and over" the lobe top, and down the other side, and AGAIN set your indicator to the SAME lift minus .050, so and again note your degree wheel.
Now you have two degree readings "some distance apart." These degree readings are now the point at which the lifter was .050 below max lift
ALL YOU ARE DOING here is picking two arbitrary lift points.......050" below max lift..........and using the idea that IF IF IF the lobe is symmetrical, then the centerline (max lift) is exactly halfway (rotationally) between whatever crank degrees indicated those to settings.
so with your two crank rotational degree settings, all you need to do is figure halfway in between those readings.
