Great score, killer basses.
i think the Sabre has, arguably, the best slap tone of any bass Musicman/EB ever produced.
From the research I've done, it seems that left handed Pre-EB Musicman Stingrays and Sabres were produced in a single production run in February/March of 1980. So I'm guessing yours is from around that time period with a serial # somewhere around C0049xxx? I've also seen about 3 times as many lefty Pre-EB Sabres as I have Stingrays, which is strange when you consider that the Stingray is far more popular. (Still pretty rare though). Interesting that your neck has issues. The one I bought from Southpaw ages ago also has/had neck issues, i.e. buzzing frets around 3rd-4th frets on E string. I eliminated most of the problem myself playing around with the truss rod and saddle height, but it's still not set perfect or up as optimally as some of my other basses.