Heads

A little extra power is always nice, and the Aussie closed-chamber heads make it easy to get a 9-1/2:1 compression ratio with flat-top (stock) pistons. The closed-chamber really means the chamber has a large "squish" area that causes extreme turbulence and mixing just before ignition, all of which are good for efficiency. Drive-ability should also be better with the Aussie heads, as they don't have the gigantic valves & ports of the 4V heads to stall airflow at low engine speeds. Your PIM headers will likely be oversized for the Aussie exhaust ports, which is also good, as the mismatch acts like anti-reversion plates without the complication or cost of extra parts. The intake also works the same way. Both will cause the engine to have more low and mid-range torque and will fall on its face above 5500 rpm, so if you regularly drive at those speeds, a new intake may be a good choice.

Jack,

I didn't think it was good to use a 4V intake with 2V heads because while it may work to use a manifold with smaller runners than the ports, the opposite is not true. I know some 4V manifolds are intentionally designed with undersize runners, but not the opposite. The Torker, for example, has a miss match designed into the manifold (smaller runner), and buyers are told not to port match the manifold.

I also think that the Weiand single plane 2V manifold is the most popular manifold for 2V heads.

Ken