I've had a different experience with the polycarbonate (Lexan) valve covers that I vacuum formed and used on the dyno...
Dyno? Are you deef or sumpin'? Put that sucker out on the road where the engine ingests dirt and slow-moving pedestrians and such, where the oil gets dark and starts to break down. Not coddled in an anti-septic crib where you goo-goo talk it and teach it to use its fan as a fidget spinner. See what that LEXAN looks like after a few thousand miles of reality. You know, the state of being that I try to avoid at all costs.
If I'm wrong, then fine. Good for you, and you can call me any names you wish, as long as you don't send the goose after me. {shudder} If I'm right, one night you will hear your customers gathering for a hanging outside like a scene from Frankenstein. Instead of pitchforks and torches, though, they will be waving pieces of unclear polycarbonate rocker cover lids. Your choice.
Alternatively, you can make aluminum pieces to fasten there for driving use, and let the customer switch out for valvetrain inspection or car showiness. In any case, don't forget to have clear distributor caps made to match, because those are really boss and worth extra horsepower. Maybe a clear air cleaner lid, too. And quite possibly a clear
And quite possibly a clear... what? Don't leave me in suspense.
In the spirit of this transparent topic, I typed those next two paragraphs using invisible ink. To see what I wrote, which is really insightful and such, get your heat gun (blow dryer will suffice), and run it back and forth on your computer monitor. After it reaches a certain temp, the words will appear like magic. No, really. Don't you trust me?
I've already had a couple customers asking about an aluminum cover instead of polycarbonate. I could certainly machine a billet aluminum cover, with fins even, to use in place of the polycarbonate. However, I have the same concerns as stated earlier, about seal. There is only room in the casting for five screws to hold the cover on. To bridge some of those long distances with an O-ring seal might be problematic. I have to test the cover first before I know that will work.
Lemmee guess, you are going to test it on the DYNO! BWAHAHAHA!
I think the clear covers would go nicely with the clear distributor cap. Then, a clear center cover on the intake adapter, and a clear cover on one of my timing covers. Moving towards the visible V-8 engine, we are...
Speaking for the forum at large, I think all of us can appreciate getting drunk and going out to the garage, lifting the hood, firing the beast, and sitting there watching the little rotor-thingy going 'round and 'round for hours. Too mesmerized to remember to unzip yourself to leak all that beer? No problem, the airflow through the factory fan will dry your jeans in just a couple minutes. Ask me how I know.