Rear Shelf Speaker on W114

[LT5PLA]

Hi all, some advice. Have a 1970 w114 250 sedan. Previous owner had added aftermarket deck, front speakers in doors and in the rear 2 6x9 speakers in boxes. Now I didn't like the look, disconnected the boxes ans would like to mount the 6x9 speakers into the shelf.

Question is, is it possible? Looks like there is some sort of extra bracing of metal towards the edges on the underside.. there is a punch out for a mono speaker but I want to run 2 speakers.

Anyone done something similar? Or do I jusy got for 6.5inch speakers or smaller and mount them more centred?

I'm from aus, so this car has the seatbelt retractor on the shelf and 2 baby capsule anchors. Which leads me to another question, how do I remove the carpet on the back shelf?

cheers