Had some spare time this weekend and designed a speaker adapter plate for 6.5" in S13 based on
this discontinued design, which I think was metal. It kind of mimics the way the stock speaker adapters angle up and back. The angle should also improve window clearance over the cheap flat adapter most places sell (or DIY).
I don't have access to a printer large enough though. I need something with like a 250x250mm or larger bed. I did print the design on paper and test fit.. the clearances are extremely close because of the part that projects into the door.