but has smaller A3 ports and no cross-over:
You can see how much smaller the A3 port is here:
That's a 4V gasket on top of an A3 port. What's not obvious is the A3 roof is higher
(obscured behind the gasket).
You can clearly see the evolution of the high port heads here:
On the left is an iron 4V modified with an aluminum high port exhaust port plate like
they ran in Pro Stock. You can see the lower edge of the original exhaust port (painted blue).
In the middle is an A3 port which is slightly higher with a more uniform round shape, instead
of the weird area changes of the iron 4V port. At the right is a ported C302B. The C302B
ports start out much smaller as you can see from this scan from an old Ford Motorsport
catalog showing a comparison of C302, B351 and A3 high port heads:
The same heads as above on the intake side:
and the chambers:
High ports share the quench 4V chamber design. The C302B head on the right has been
clearanced for a domed piston.
Dan Jones