To adapt your rear speakers from the 4x6 small ones and put a larger 5x7 in their place. Mirror for opposite side. Designed for Phoenix Gold SX57CX speakers (Great Speakers, worth the $$) . May want to reduce flange cut depth from 3mm to 1.5mm, Size is 200mm x 146mm x 31.75mm. Will fit on 165mm X 145mm bed if you use the split in half version and use 4x 1/8 diameter pins and epoxy parts together. Original solid works file included for customization. Probably best to pick a black or gray material.
I recommend that you hand tighten or thread screws by hand into frame due to fragile print and watch screw size and adjust hole as required.
Uses twisted loft between the two sizes. Rotated and offset to fit into space in car.