i have a set of low mile OE 559 heads in the shop.
with the factory valve and valve job.
on a 4.250 bore......as i recall, they only flowed like 285 @ .500 lift.

i had another set in the shop not too long ago, fresh radius type valve job and bowl blend from Barton, Manley valves......i think they were in the 330's.

i'll check my notes to verify the numbers.