I dont even think I'd bother with MOB, just go to Repco, Supercheap or something like that. If your going to be only spending $50, their speakers will be better quality IMO as they have more purchasing power than a smaller trader like MOB.
For sure take the stocker with you to make sure they are about the same depth, otherwise the power window glass will end up contacting the magnet/back of the speaker, NOT COOL!
The stock white speaker mounts are not very accommodating for larger magnets or deeper cones and you may need to grind some out of them, its very easy though.