Well, I removed a door panel and I found out that one of my speakers is damaged, the cone does not move freely anymore. So I did not put different speakers in the rear doors. I did test the fit of the Scosche part, and here's what it looks like where the screw goes to the door.



The screw is just a little too high for the nut on the door, but by pushing the top down to flex the plastic, it fits. I would suggest getting the gasket and foam like the OEM mounts have too. Otherwise, everything seems okay.

I tested both of my JVC speakers and the one that wasn't damaged seemed like it was playing high notes from the songs that happened to be playing at the time. I didn't check with test noise though. It seems my JVC speakers have some kind of built in low pass filter because they would not play any low end, unlike the OEM speakers. Is this likely a design of the speaker, or is there something about speakers beyond a one-way that don't play low end?

I also looked again for a place to put a wire through the firewall and I'm not seeing any existing holes besides the one just about the brake pedal. I see some knockouts behind the pieces of sound deadening, but I don't want to drill through anything.