I have two theories on this one, of course all without being there, so it's all really a WAG
1 - It had a minor misfire or crossfire on top that fooled the O2 sensors into thinking it was fatter than it was, as you guys ended up with far less jet than I'd expect with a 780 and more timing than I'd expect it to need with that chamber indicating it was a little lean too.
2 - The carb wasn't opening all the way, even after you tied the linkage, which did something funky at the boosters that caused the abnormal jetting. Building vacuum would indicate a carb size or throttle blade issue and could cause some puddling of fuel which made the mixture goofy and held power back
If neither of those are true, that lean of a jet could be an indicator of an HSAB issue that was making the booster come in too hard and too early, however, that alone wouldn't keep the power and RPM peak low, so I would go back to my evil theories
Too bad you guys couldn't have got a known good and BIG carb on it. I don't think a 780 alone would kill the peaks on a 445, but it would have been good to see what it did with a known good carb and a little more airflow