Our short scale strings have a 37.25" winding length, outside of ball end to the silk. Anyone with a Mustang bass can take a measurement of a string currently on the bass to see if they'll work. I don't have a Mustang in the office, or I'd do it.
As a point of clarification, I worked with Scott Whitley, who was the originator of the SWB-1 (before Chowny took production) and head of Link Removed. We got to talking, and I asked if there was anything we could do to edit our short scale strings, and that's where the talk about the winding length started from.
The original SWB-1 did not have a thru-body bridge, so there's a good chance that the short scale Balanced Nickels will only work with the top-load option on the current Chowny SWB-1.