Nice color!
73 would have been early in its run. The Mustang dates from the 60s, the Musicmaster didn't start until about 71.
Looks like a Badass bridge, which would accommodate the polepiece spacing of the 51-style pup. But that's wider than the original bridge spacing, which was narrower because the neck width at the heel is Strat-width, not bass width. Any problems with the strings being too close to the edges of the fretboard?