So all Leo did for young Sterling Ball was make a "5 string" pickup and install it on a 4 string bass? No super-cool specially voiced circuitry? So, I could get a aftermarket MM 5 string pickup, a new pickguard, and if I route out space, I could install this on my OLP MM copy? Again, is that really all there is to it?
This would be a good question for the EB MM forum on the, well, the EB MM website. I've gotten great specific info on Music Man basses from there. I have yet to check out an Old Smoothie, but I hope to before long.
When Leo was inventing the musicman it's worth noting the pickup likely uses Alinco poles, so if you're going this way you may consider avoiding the ceramic or neo offerings. I'd warn against this unless you're sure you want a bass with no attack or tone... I've never played a real EB Ol Smoothie so take this for what it's worth, but I've experimented with different string spacing and pole alignment on a MM. When those poles are right under the strings the sound is punchy, defined, and bassy as we've come to know the musicman sound to be. When they're off even a little the fundamental sound drops off quick and tone suffers so much. No doubt, Ol Smoothie sounds smooth but that's because it's missing all but the deepest frequencies the strings can inflict on the coils when they're so far out of the magnetic fields focus. One of the Ol Smoothies was for sale on TB (I can't remember who was selling it) and at no surprise to me, it already came equipped with a regular MM pickup the original "smoothie" pickup was in the case. YYMV
My experience differs. I got plenty of attack here, on all but the A string, and it was just barely less punchy than the others. Entirely giggable. This was a Duncan SMBD (ceramic) pickup.
The Fender Roscoe Beck Signature basses do a similar thing with the pickups, I just remembered. I also remember coveting my students' Roscoe Beck V.