All the numbers look good to me...
Was it red hot like that when you were testing?? I wouldn’t rule out the alternator, and that positive cable should be replaced due to the heat...
Load test the battery, just to be sure... a static voltage reading isn’t a guarantee. Try overlaying the positive...
Do your negative side voltage drop from the alt case to the battery negative post. The reading will be interpreted just like positive side, the lower the better.
Great job with the voltage drop tests...
I was struggling with your chicken scratch... was there a ground side voltage drop measurement taken from the alternator case to the ground post in the battery?? It looks like you mentioned engine block and alt bracket... those are grounded, but the end...
Is the fuel old?
To 100% rule it out I’d drain it and start fresh.
Do you have an oil pressure gauge? Is oil pressure ok under load?
If it were me I would:
Confirm good oil pressure
Drain fuel and put in fresh
Check ignition timing
Adjust valves