anyone ever flow test 383 A body manifolds say vs 383-440 hp manifolds

My understanding is that the difference between log manifolds and B-body HP manifolds is about 5hp. The other difference between a 350hp 440 and 375hp is the cam and carburetor. I don't know about the cam specs in the 1967 A-body 383. The claim from the factory was that the 280hp was due to the manifolds (considering the above I find that very hard to believe). 1968 is even more interesting. Reports are that NO 340 came in under 320hp in the dyno room, but could have that and rate the 383 at 300 like they did that year. Same reason they couldn't keep the 1967 280hp rating. 1960s horsepower ratings were based more on marketing and insurance rates than they were from reality. It's doubtful that there is much difference in HP between the logs and A-body manifolds.