Install 4V valves (stainless one piece of course), open up the bowls to match, narrow the guides, gasket match intake port to manifold, leave the exhaust port exit alone. This is good for over 400HP peak without noticable low RPM performance loss, and only about 8 hours grinding with a carbide cutter. If you want more HP, work on the roof of the ports to increase flow at the expense of low end. Good luck.
I've ported a couple sets, and have noticed the chambers are really tight. Valve shrouding seems like a problem even with STOCK sized valves. Unshrouding the valves in the combustion chamber should be worth quite a bit of power... especially when using 4V sized valves in Aussie heads. I would consider it MANDATORY with those.
If the port work is good (and those aren't the simplest heads to work on) the Aussie heads work just fine... especially on heavier cars and/or smaller displacements.
If the engine is larger (stroker), the car is lighter, or there isn't much port work planned, you'll probably be happier with the closed chamber 4V heads... especially with a 6500-7000 rpm upper limit. For a 351ci engine that rarely goes over 6k, the Aussie heads would probably be best.
These are just MY opinions, and reflect how I drive my hotrods around. (hard and aggressive) The carshow and 'putter' crowd, who run small exhausts and rarely spin their engines to redline might be a bit more conservative.
All serious Kiwi's running clevelands use aussie 2V 302 cleveland heads. Haven't needed to unshroud the valves on any steet motors yet. We comfortably spin our street engines (in 3500lb aussie falcon cars) up to 6500RPM with just the small amount of work I mentioned earlier. We also ran a cleveland 3 years ago in an altered and it would rev to 7000RPM with aussie heads, and minimal unshrouding work. For a strong street/strip application, you can't beat the aussie heads.
Now, our latest motor for the altered does run 4V closed chamber heads, but it will also spin up to 9000-9500RPM curtesy of a 305 duration (at 050) comp cams heart.
This is all from real world experiences. Take from that what you want. Good luck.