To modify the stock 4BW bumper for the dive planes means you have to cut 5 slots on each side for the dive plane tabs to engage a support on the back side. The stock bumper does not have the support, so until someone markets a matching part, you'll have to get a factory slotted bumper. I ordered one at a local GM dealer at MSRP and it was $300 + $75 core + tax (F Fascia - GM 85153560). You can probably return the primer bumper as the core after removing the bracket supports...
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Removing the support is easy. I used my Harbor Freight trim tool kit, slipping in one tool from the bottom and another from the top on the outside top weld. After it popped you can just pull on it and the others broke loose one by one. If any stick, you can use the trim toll to help it along. This is the result:
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With the support removed, you now have to cut the slots in the existing bumper. It is convenient the standard bumper provides markings for both the support outline and the slots, so you don't need a template:
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The outside slot support is already provided in the standard piece shown in red above. You just need to cut the outer cover there. I had already stripped my standard bumper because I tried using the new bumper, but I didn't like the color match and decided to re-use my original with the modification. That made it easier to lay the bumper on its face to mark and cut it. The curved shape is still tricky, and I propped the upper side to the back of a chair using microfiber where the bumper touched the carpet or chair to protect the paint.
To help see the slot markings, I outlined them with tape. There are double lines for the slot markings. Use the outer line to tape and cut.
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I found the fastest and most effective way to cut the slots was to use a Dremel cutting disk to slot through the middle of the slot, then use a sharp Exacto knife to shave (not cut) up the the edges. Use it like shaving dark chocolate curls for baking, pushing the blade through as you push it forward. As you get to the ends, use a RotoZip tool bit to round the ends. I felt rounding the ends would reduce chances of splitting a sharp corner might cause, and matches the OEM slots. With the grill parts installed, you may have trouble using the Dremel cutting blade on one of the slots. You may have to use a 1/8 drill bit, then RotoZip the slot enough to use the Exacto blade. Do all the work from the back side so you don't risk scratching the paint on the front. The finished slots looked like this:
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Finally, I used the dive plane to locate the support bracket to verify the fit. When I was happy with that I scuffed the back of the bumper and face of the support with sandpaper and used J-B Weld 50139 Plastic Bonder Body Panel Adhesive and Gap Filler Syringe applied at the previous weld points, then used the clips to hold in place while it cured. When you first apply it, you can shift the support bracket slightly to match the outline perfectly. The factory installed bracket didn't match the outline as accurately as mine did. This is the result of the epoxy attachment, and it holds better than the factory weld.
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Then for me it was just a matter of moving all the grill parts back over again, and reinstalling the bumper cover. By the way, I never jacked up the car to remove the bumper. You can get to all the screws easily without doing that. And just turning the front wheels one way or the other at the start is all that's needed to get the wheel well screws on both sides.
The final result turned out great, and I have matching paint again
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As a final note, I used factory OEM dive planes. The tabs on the OEM dive planes are a consistent 2.4 mm thickness. If you use non OEM dive planes the tabs may be different and require either wider slots or thinning of the tabs. I suggest test fitting the dive planes with the factory slotted bumper before you remove the inner supports. You'll also need 10 clips. I used these on Amazon
https://www.amazon.com/dp/B09PRDWDWG?psc=1&ref=ppx_yo2ov_dt_b_product_details . They are physically identical, but seem to be a different (harder and potentially more brittle) plastic. But I installed and uninstalled the clips several times and they held up well.