mid bass front stage

Frequency response of the driver isn't an issue by a long shot when your intention is to bandpass it.  It would, in fact, be taking the place of the component mids in the bass freq range, so that would be from ~80 Hz to ~500 Hz.  Any 8" driver will perform in that freq range, but mixing it into your system is where the going gets hard.

Driver orientation is a key factor as all front drivers should be grouped closely together  It is much easier to fail spectacularly with a homemade 3-way front than to pull it off easily.  You should first set up your best possible 2-way component frontstage before endeavoring to add the dedicated bass driver into the mix.  This includes, of course, the damping of the car's metal in the important areas.  By adding the dedicated bass driver, you will also encounter the need for additional gear that will be needed for managing the crossovers and more sophisticated testing procedures than normally needed with the more common (pre-designed crossover) setups.

haemphyst's new system is a thread you should read.  It will answer many of your preliminary questions and help prepare you for a project that can go on for a long while.