now that you have that hole...I'd glass the bottom of the door and keep your drivers closer to the front. Maybe using the space that you made for a sealed/ported area for midbass?
Even if you go with a 4" driver to go in the factory locations, that's still very poor placement of that midbass driver you have installed at the rear of the door.
If you want to go 3-way, 'glass the smaller components (4" midrange and tweeter) into the kicks and mount that midbass driver in the factory locations.
ooooo, that is just so wrong I hate to say. Get that speaker out of there and put it up front where it belongs. Seal up the hole and make a proper baffle board for both mids.