didn't intend to sell the original spoiler in any case, long since learned to keep everything i've taken off of a car in case they go up in value decades later, tossed a engine block on my 69 charger r/t when i was 21, wish i had it now...would add 8k or more to the value of the car i still own 33 years later.
When i first started, i wasn't sure if there would be room inside the spoiler for a camera, and hacking into the original didn't sound kosher to me so i bought one from takeoffparts to "experiment" with, the srt8 spoiler is slightly taller than the original so it also gives a little more room to work with inside.
Also, when i first ordered the camera, the license tag version was sold out so i was kind of forced to think outside the box. One note, it pays to hook up the camera before you mount it once to make sure orientation is correct, in my case it was mounted with the arm/brackets downward, not sure if i had to spin it inside the mount prior to mounting inside.
Oh, as a side comment, what i did pretty much anyone could do, I'm usually pretty lazy when it comes to working on my dd car, taking it to a shop for most work to be done, I figured removing the spoiler and bolting on another wouldn't be that hard, getting bolts off was simple, getting thru double edged tape was a bit more challenging, helped to have some plastic trim tools to use. Finding dead center was easy, there is a middle clip, and i used a piece of 3/4 inch masking tape wrapped around the center point so i knew where to drill the hole, used the largest normal drill bit in a set and drilled it in the center, then used a cone shaped stone (looked like a sharpening stone) to sand out the diameter to match the lens. Just had to be patient and not bear down too hard with the cone stone, it would eat thru plastic pretty fast.