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

How do we really know if there an hp difference between A and B body 383's factory gross hp number are unreliable, could of rated them different for sales/insurance/competition etc.. I guess the 4 gear 340 cam makes no more hp than the regular 340 since there rated the same hp or 340 carter avs vs thermoquad.

I'm sure there's a slight difference between manifolds but since we have no dyno comparison we won't know, but judging from what dyno shootout of other manifolds and shorty headers and even long tube headers over the years I would think probably 1-5 hp and 10 hp max.