G&L and slide bass set-up

Use a fairly heavy slide. You may want to go to a lighter string set.

Try D G D G (E and A strings down a tone, others standard).

This gives you an open G (no 3rd). Good for straight power sliding. And you can use a normal string set.

If you want something a bit more melodic, and you're happy to play around with string gauges, try D G B D (low to high). Use an A tuned down for the G and a lighter A tuned up for the B. This gives you an open G with the major 3rd and also gives you access to partial minor and 7th chords with the slide.

As you can tell, I like tunings with the 5th on the bottom as it lets you slide up to the root, and also do descending things in the bottom.

 

Slide bass:

I converted a bass years ago, and still play it occasionally. I started out with four strings, and apparently that was outside my range of talent. I then redrilled it for three strings and pulled the frets. Don't worry, it was an Ames with a neck that was warped and far from a fit for the body. I drilled the bridge for a string inbetween the current 2 and 3 strings, and cut a new slot in the nut. I tuned this in fifths, for easy chords. I setup the bridge so the middle string was significantly higher than the others. Eventually, my modification 'undid' itself so I ended up with a two string, tuned in fifths.

 

D-A-D-F# (low to high) gives you open D, which is nice because the root stays in the bass, while still providing the 3rd AND not really needing any different strings.

As to the G&L, I have an older L-2000 that is as nice as any new one I've played. If you dig the old SB-2, why worry about it?