One of my favorites...I learned SO much from that guy.
The dude played an amazing variety of gear, for one thing..... he had about a warehouse full of stuff and he used pretty much all of it at one point or another, and changed things around pretty frequently.
here's PART of his collection:
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with the Allman Bros he used primarily Alembics, a Modulus, gibson T-birds, a few Hofner clones, etc, and once in a while a 12 or 18-string.... he used the 18-string on Whipping Post, ala the Great Woods DVD. He used an Alembic preamp-- I think an FX1B-- and a Crest poweramp and a variety of cabs.
With Mule, he used primarily old T-birds, EB-3s, Eb-2s, EB-0s... basically if it was a Gibson bass, he had it and used it. The amps he used with Mule typically were a 70s SVT with 8x10 and some other amp-- sometimes a Marshall, sometimes others-- for distortion. He also had a hodgepoge of custom basses-- doubleneck bass/mandolins, a 12-string Flying V bass made by Chandler, etc.
He mostly played with a pick with those two bands, but he was also a competent fingerstyle and slap guy. He also played several other instruments quite proficiently.... He really had the whole 16th-note thing down.
Here's a couple articles that might help ya: Invalid Link Removed
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12stringbass.net also has a tribute page for him under the 'players' section.
What other kind of stuff are you looking for?