Stereo speaker location suggestions

[OUbesto]

I am looking for any suggestions as to where I can mount some stereo speakers in my '70 C10.

PO mounted them in cutout on the driver and passenger side kick panel walls (see photo). Unfortunately I do not believe there is enough depth to mount some decent 5 1/4 sized speakers. I tried the plastic molded kick panel speakers from Brothers but the speaker sticks out too far and it interferes with the parking brake when depressed. I thought about installing in the door panels on the bottom metal area below the upholstered door panels.? My gas tank is still behind seats so no room there....Any thoughts?