And of course you can hang all the 2.0 turbo bits and make 300hp easy...

The 2.4 is an oversquare motor with a longer stroke than the bore is wide, like the 2.6, so it makes a lot of torque. The 3.0 is an undersquare motor, so it turns rpm easier, and makes more power higher up.

The 2.4 makes more power than the 2.6, and about the same torque, because it breathes a lot better and has a better cylinder head, especially in the 16v form.

The 3.0 makes more hp, but about the same torque, albeit at higher rpms. The fact that the torque peaks higher is probably the source of the higher hp, since hp = (torque x rpm)/5252, so if you make the same torque at higher rpms, you automatically make more hp.

The 2.4 is not a straight bolt in for a 3.0, but the wide block is a straight swap for the 2.6.

For 2.6 to 2.4 swaps, see projectzerog.com. It's common for the starquest guys.