The guy in the current JGB lineup with Melvin and Stu plays an actual Steinberger and gets a tone that doesn't even really resemble John Kahn's. IMHO I'm getting a lot closer on an ash-bodied, maple fretboard J-bass copy with a good mid-scooping preamp.
I think the Steinberger takes too much blame for John sounding muddy, I think they buried him in the mix on purpose due to all the H destroying his playing. In Live at Shoreline it's a crime.. you can hear him under the verses and choruses but he just disappears in jams. Check out 4/24/94 at the Warfield on the other hand, It's the same tone but he's a lot clearer, he plays a lot better, and you can hear him pretty well.
Plenty of pics of the G&L on The Jerry Site, it's definitely an early L2000. In some pics it looks brown or blueburst but I've seen ones where it's definitely solid metallic blue. Go to the Gallery and start at page 30 and you'll see it. http://www.thejerrysite.com/images?page=30
That's super cool that you saw him in 81!!! You must have seen this bass:
I modded my old cheap but good P-copy to match it and it does rip right through a mix. The trouble is that lately I'm a little TOO loud in the mix so I want something warmer and rounder. viewtopic.php?f=309&t=8038&hilit=john+kahn
My other motivation is practicality... my J-bass is a pretty expensive thing to drag out to a Fennario show just to play one or two songs, and my modded P-copy is unreliable... it needs nearly constant truss-rod and intonation tweaking to play well. I'm really looking forward to the graphite-reinforced neck on the US-made Fender.