Update 2:

Well I finally fitted the woofers to the original brackets only to discover 2 large issues. The first one is that the magnet was so large that it did not fit into the metal opening in the car.. The second is that the front of the woofer creating positive waves was open to the back creating negative waves (in other words, the woofers are no longer sealed due to the heavy modification needed to fit them in the brackets). Overall this means that the brackets are pretty much useless for this project.

Therefore I am currently looking at possibly making an MDF/MAF Bracket which would have the front of the woofer facing toward the seats with the magnet facing the trunk.
I did get a chance to plug in a woofer and test it - it seems to be a perfect match audio wise.

I'll update again later with the results of whatever bracket I make, etc. It may take a while.

Kolme