Over on PY forum (Tom S mentioned that "repos don't have a heat riser if I remember?Tom")
THEN b-man replied ( "Heat riser flap side is always larger at least on the standard log manifolds. The opening for the flapper is machined to about 2.10’’ and the other side as-cast opening is about 1.90”. On some of the earlier style log manifolds manufactured without the flap there’s still that same difference in outlet size between the right and left manifolds. It wouldn’t surprise me that the openings are different by about 1/4” on the long branch manifolds.")
AND joe's Garage reply ( "Unless someone has started reproducing them EXACTLY.
And remember that the 1969-up long branch manifolds - like those on our (two) 428HO 1969 Grand Prixs - didn't have the flapper either.
We've got an extra pair of manifolds off another 428HO GP - I'll dig them out and measure the outlets.")
So from the info from these three fellas GREATLY APPRECIATED it is that the passenger side is larger output probably due to the flapper valve, so that would work out the same flow as the left side with the 2.25 output... I hope they don't mind me sharing there knowledge
My memory is not what it used to be since my strokes so take this with a grain of salt. To me it sounds like you have manifolds from 2 different manufactures. If I remember correctly the only manufacturer producing larger than stock 2.5 inch outlets is R.A.R.E. and the rest use the stock 2.25 outlets.