1: DV uses LSA as a basis for cam selection. He states this is a starting point. Overlap is then a function of lobe duration. You may get better performance with the correct LSA and a bit less duration.
Regarding the statement of DV's information coming from mainly testing Chevy engines is not exactly correct. Now the shear number of SBC and BBC engines produced makes them highly accessable, so yes he has tested a lot of Chevys. But he has a lot of experience on Ford, BMC and some Mopar among others. Now one point to remember is engines are assemblies of parts essentially the same. Canted valve, hemi, wedge and 4 valve present different characteristics, but within each class they will respond similarly.
2: His formula is cylinder displacement/seat diameter not valve diameter. Thus the intake head diameter × 0.91. DV also says a correction based on quick "off the seat valve motion". This relates to low lift flow. Yes a fully ported head will flow more than an unported or moderate ported head. This will just complement the proper cam LSA selection.
SBC - 128 - (cyl disp/(valve dia × .91))
SBF - 127 - ( cyl disp/(valve dia × .91))
SBM - pick one. They are all inline valve heads.
Canted valve - 132 - etc
3: Richard Holdner's cam test pretty much confirms what DV states.
For corrections, CR will indicate tighter or wider LSA. DV goes into that. Lobe profile and high ratio rockers have a bit of affect, something like .25° to .5°. Rod length/rod to stroke ratio makes virtually no difference. That said a long rod tends to be quieter and aid hi RPM torque (power) while a short rod tends to more noise from piston slap and promotes a slight advantage in low RPM torque.
DV does state that testing single cam engines to determine the best LSA for the combination requires dyno testing and a number of cams with different LSA's to test and then play with advance or retard. This is getting serious at that point and way beyond a street base build would require. But for a race car where every single lb/ft or HP advantage could be the difference between the money or shame, it is important.
Now if you read Billy Godbold's book on Highperformance Camshafts and Valvetrains, he talks EVO, IVC, IVO and EVC with LSA as a consequence. I would expect Billy through his years in the business has a more intimate knowledge of camshafts than most of us could hope for. I did ask DV if he had read Billy's book and if he had an opinion. He wrote back stating his intention to read it and then possibly comment. A discussion between Billy and DV could be interesting.