Does anyone know roughly what year this happened? Around what time did they start making 5-strings and did any of the 5'ers have a 3 bolt neck or front mounted electronics?
Their first 5 string came around 1988 - the L-5000 had really tight string spacing. They started making a 5 with normal string spacing around '93 with the L-5500. By '95 they brought out the L-2500. The L-5500 and L-2500 always had 6 bolts, early on they had neck plates, too. Around '97 they changed the headstock from 4+1 to 3+2, made the bridge string-through, got rid of the neck plate and went with neck screws with ferrules, and changed the body shape slightly. Sometime in '98 they started switching over the 4 strings to 6 bolts and the same body shape change.
Main difference is the pickups. The L-2500 replaced the L-5500 when G&L started making their own MFDs for 5 strings. The L-5500 had second-party pups, but I forgot who made them. I know that they were a standard sized 5 string soap bar pups. There are a few MORE differences, but they are slight.
I used to play an L-5500 everytime I went to this one crappy music shop that had a NOS one. It had EMG pickups on it and the string spacing sucked. It wasn't a horrible bass, but if you don't guitar-like string spacing, I'd look elsewhere.