So, I ended up with a rather unique airbox by happenstance. I held off on the Evolve airbox because I wasn’t comfortable that, 50 years from now (at which time I still intend to own the car), it was certain that Evolve would still be around and I would still be able to source filters. A while back, Sal asked me if I would be interested in their development box, as it uses CSL filters. I said yes, and that’s what’s on my car. I had assumed till now that it was an Evolve airbox, just an earlier version, because it had the Evolve style ducting.
Yesterday it was brought to my attention by a fellow forum member that the box I have is actually a (pretty unusual/rare) Die Wethje airbox (Die Wethje was the OE manufacturer of CSL airboxes for BMW. They made several variants including the P54 (racing variant of the S54) version, the CSL version, the version my car has, one that has a bit larger/beefier with the big inlet, and possibly the one where the filter that slides in from the top.
I stopped by to visit my (still roofless) car, and sure enough it had the same stickers (this is not my airbox, just using the pictures as they’re the same stickers):
Pretty excited! I have nothing bad to say about the Evolve airbox, but actually having an OEM one makes me pretty excited!