OK, here's the hiccup, and why you won't find one at the Donaldson Dealer. From an email:
Justin,
Just another note of clarification; the unit we sent to you was actually an experimental modification of the P/N PCD100028 used in a compressor application. A silencer plate was removed from the original unit to eliminate as much restriction as possible for your application. If this were to be released to production for automotive use, a new number would have to be assigned for your version, and depending on the potential qty. , the outlet tube could be modified to reduce right down to a 4" outlet to eliminate the need for a 6" to 4" reducer adapter that you describe as a challenge to fit in.
So, this is STILL a prototype. It's not yet for sale. Donaldson has some internal handoffs to make before this can become a reality. The division that should be selling them to us is their Commercial Automotive division. My rep was NOT from that division, and while he has been VERy helpful, he can't legally sell me something.
Oh well, I'll keep working on this and let you know when/if it's coming to a Donaldson dealer near you.
jlh