Verismo, I don't pretend to be a suspension expert by any means, but after reading this I'm wondering if you didn't hit on it with your other thread about rake & trail. Do you know what the R & T is on those Indians? Maybe, just maybe that difference is making the front wheel of the "B" react in more of a straight line to the handlebars thus causing that roughness, whereas if the Indian's wheel was reacting to bumps in a not so direct path to the bars, the bumps would be soaked up so to speak by the geometry of the front end.
Just some thoughts, I really have no idea.