Yes, the new cover design plays a large role in the improved flow and map of the new wheels. As for being retrofit, I don't see why not, but need to swap one to confirm.
Been getting great feedback on these so far. Have a 369 out there on an lbz with 100% injectors and 10mm pump, tuned to try and keep stock motor happy. Owner says it spools quicker and cleans up more smoke than his billet 366 did
I spent a while yesturday talking with the Borg guys yesturday at schieds. He said there is going to be a release of some new 400 & 500 framed models. I want to do a 369 with a 484ish size. He made it sound like we will be seeing them by end of the year.