Well...I also researched what flat wounds are suited to this bass, the tuning peg compatibility being the important detail. I can't remember which brand it was, but they're never coming off anyways.
The reason why I removed the stacked controls - I often tweak the controls while playing a song and I just prefer simplicity and this mod lets me do it faster. I wired the pickups in series because it's another preference of mine which I learned from my Stingray. Stronger tone and volume.
I haven't tried any short scale flats yet, that wouldn't work with the tuner posts on my lefty '18 Longhorn. However, I can't speak to the American originals - or the later Chinese ones. Mine's Korean... The only flats I can think of, that might not work, are GHS's Precision Flats, since they're made considerably longer than the rest of them. TI 324JF's might be another one; those are long enough to fit my 30" scale '94 Gretsch Broadkaster. Which can wear most LONG scale strings with no problems at all - and has... My Longhorn currently wears La Bella 760FX's; no problem at all with those...