JM,
Nope i don't have an answer for you. Sorry.
I am not sure if the '03 4runner's HU area is a 1.5 or double din. If it is a double din, then you probably can fit those two decks (assuming that those decks are SINGLE din each). You may have to go to your car audio installer to check the size of the 4runner's Hu area.
Sorry...hopefully, someone else can provide a better answer.