I remember it too, vaguely.
My answer as I run some classic and new combos on the Gonkulator is,
It Depends!
I find the best split is anywhere from 3 degrees to 16 degrees, but in no case is a single pattern the best.
The best split depends not just on the tntake vs exhaust flow in the heads, but on the whole intake vs exhaust tract.
And of course it changes with power adders.
The Gonkulator thinks that both the 390GT and 428CJ like about a 4 degree split, ie 212-216 duration works better than the factory 207-221 duration with its 14 degree split.
But that's with open exhaust.
Thru mufflers, they all want more split. Maybe that's why Ford added some split for the 428CJ, and it ran so good on the street that way.
Its pretty obvious as an example that Fords last hipo big block, the 429SCJ, should have had a split pattern cam, with its sewer pipe intake ports, football stadium sized intake, and pinto-sized exhaust ports. It Gonkulates best with a 16 degree split, and would have probably smogged cleaner too. A 460SCJ with a 16-degree split cam would have been the true equal of the Chevy LS6 that year.
So it just depends!