First off, thank you for the amazing compliment!
Used oil caps can be done but the heat will vaporize the inner steel wool. They can be repacked with some new 00 steel but it's a bit tedious.
The black wrinkle I use is a really good replica for vintage parts; purists report it can usually look better than factory due to the texture being more even. These were done for our Swedish member Ulf (65dartcharger), the Technical Director of the International Chrysler Collector's Association, several years ago. His car scored 996 out of 1000 at MCACN and it's my understanding the valve covers were NOT one of the deductions.
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That particular powder has a lot of leeway and can be heavier / wrinkley-er (is that a word? lol) depending on particular tastes. I like to shoot it on humid days because it turns out spectacular.
Give me a call if you want to go over the details!