El Caminos (I think up till 1988) and Malibu wagons (and its siblings) from the late 70s and early 80s had taillights in the rear bumper. Probably quite a few other vehicles did too. I've seen the Vette bumper kits on trucks too and I don't see why it wouldn't be legal.
If you stick a 3rd brake light on your aerobed, that'd probably help your own safety too for people that don't expect to see the brake lights in the bumper instead. Even though they weren't required for trucks/vans in 91.
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Winter daily driver, parked most days right now

Summer daily driver
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