Interesting.
Like i mentioned the car was factory radio delete but I didn't mention a dealer put in an aftermarket radio and speakers in when new. The speakers are in the rear panels that cover the rear wheel wells facing generally upwards. There just isn't enough room between the panel and the wheel well to fit a normal "new" 4X10. The aftermarket dealer installed 1980 speaker is on the left side, new normal one on the right.
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Speaker grills are the black things in the wheel well bumps. Are they even in the right spot?
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Wow! That's a significant difference between the two speakers. I see what you mean about the one on the right being a deeper/taller unit.
Whoever installed the speakers initially, did place them correctly over the wheelhouse.
I suppose if they weren't so tall, you might even have been able to dent in the area slightly where the magnets would make contact.
Your other option would be to enclose them, or a pair of round 6.5" speakers in the rear side compartments.
Incorporating spacers under the speakers would look funky....but not in a good way.