I've read that too. His sound on Ballads and the Hartman date is not the sound one hears on Africa Brass, for example. I wonder what he did to his Otto Link? As far as adjusting the physical qualities of a mouthpiece, I thought the main practice was trying to increase the inner bore size, if just by millimeters. I know Steve Lacy did that with his soprano mouthpiece, and then used an alto ligature (which wouldn't affect the bore, but would allow the reed to vibrate more freely) in order to get the most open soprano sound possible.
Back to rare-ish Japanese compilations, this one looks good:
I would spin this comp!