A few years ago there was a magazine article where someone was
offering CNC ported 906 heads. I believe it was Muscle Motors.
As I recall they were reported to flow something 312cfm on the intake
side. I've had a set of those in the shop, just as delivered from MM
with 11/32" stem valves, 2.19 intake and 1.81 exhaust.

Lift------in/ex
.100----68/61
.200---145/109
.300---241/145
.400---256/171
.500---284/191
.600---290/204
.700---288/204
.800---290/205

On my bench, while not 312cfm, that's still a very good 906 head,
and as big as they looked, it was only like 217cc's as I recall.