I think that I have a bad adapter. I have ordered that Gitzo Bushing from B&H and hopefully that will solve this problem. FWIW, I think that the 5/8" "Microphone thread" is NOT the same as a fine thread 5/8"-18 bolt. That would explain the bolt not threading in the akg bar. And the threads not matching between the Bogen 3/8->5/8 bushing and the mic adapter would lead me to believe that i have a bad 3/8->5/8 bushing.
I will post back here for completeness when i get that new adapter. Thanks for your help!