Alternators are different. GC8 has a 2 pin square plug, GD onwards has a 3 pin oval plug. (Prior to 94 Subaru's had round plugs)

Rich, if it aint broke, dont fug with it.
Jappo car batteries are twice as good as the battery you will buy locally, something to do with actually putting lead in the Jap ones versus cardboard in the Aus ones.
Nothing wrong with the small battery unless you have increased the electrical load in the system. The big ones make the car harder to work on. If you must change it to a big one for whatever reason, seek out a genuine battery clamp, FFS don't fit one of those Supercheap plastic universal pieces of junk clamps.