I don't think those smaller holes on the inner side are drain holes, maybe for locating the part in a fabrication machine at the factory.
No idea what that big dimple is for either. I don't think it does anything for structural strength.
You did a good job of duplicating it. Wow $80 now? I paid less than $35 for each on mine, although it was back in 2015.
[on edit] Jim Carter still lists them for under $35, but I don't blame you for building your own.
[another edit] LMC sells them for about $25.
My bad, I was thinking rocker panels in Canadian "pesos"at $80. I have a hand lever parking brake, guess that's why I didn't realize what they were for. One of the slotted holes did have a rock hard rubber delete in it, but I didn't realize it was a delete. By the way, I never think of LMC when looking for parts, I usually look at The Filling Station, Chevs of the 40s and Jim Carter.
