As a point of reference, these are the intake flow numbers for a
906 "F" head dated 10 11 8. While not all F heads are great, the
best flowing untouched 906's I have tested have been F heads.
This particular head had a very well preserved OE valve job and
Is tested here with an OE valve and no back cut.

Intake test only-
Lift------In
.100----62
.200---122
.300---179
.400---214
.500---224
.600---235

On a head like this, once you start to blend the bowl and increase
the potential for more air to flow through the port, the short turn will
become a limitation and the port will go turbulent, usually between
.400-.500 lift, and the flow will drop off unless you start reshaping
It.