Probably the biggest limitation of the Musicmaster/Duo-Sonic was the three-saddle adjustable bridge. A couple of the more creative solutions I've seen are on this page; be sure to also check the MM-to-DS mods gallery for some more examples. Also listed are some more drastically modified MM/DS guitars, one of which is mine.

Bridge-only mods

• '58 Duo-Sonic with Bigsby vibrato tailpiece:
  front | body, front | replacement bridge | Bigsby vibrato | back
  headstock, front | headstock, back
  "When I picked it up in Tacoma about '95 it was already covered in the snakeskin vinyl seen here." Subsequently modified with a new bridge and tuners, then the Bigsby. "ps for some killer Duo Sonic sounds be sure to check out MAGNAAFLUX and THE RON DANGLE 2 MP3 offerings."
  Owned by Mike/Rinso Records
  
  
• '61 Duo-Sonic, in "maroonburst" with hardtail Strat bridge
  front, in case | body, front | body, back
  headstock, front | headstock, back | butt of neck (dated 10/61)
  Source: unknown (eBay)
  
  
• '64 Duo-Sonic, in "maroonburst" with vibrato bridge (SN 14369):
  front | body, front | back/heel | headstock
  I can't imagine how much work this was to install!
  Source: unknown (eBay)
  
  
• '64 Duo-Sonic II, in white with Tune-O-Matic bridge (116 k)
  The original bridge was moved back and is now used as a tailpiece
  Source: unknown (gbase.com)
  
  
• '66 Duo-Sonic II, heavily modified (SN 135358):
  Refinished in "orangeburst"; roller switches removed for a toggle switch; replacement Badass(?) bridge; Sperzel locking tuners.
  front, in case | body, front | detail, bridge | back, in case | body, back
  headstock, front | headstock, back
  Source: unknown (eBay)
  
  
• '95 Duo-Sonic (Mexican re-issue), with humbuckers and hardtail Stat bridge
  Owned by the Zen Pharaohs of Ultimate Love
  
  

Other more drastic(?) mods

• Teak-bodied custom-made MM/DS-based guitars:
  Glen Evelyn with a teak "Duo-Sonic" | teak "Musicmaster" | teak "Bronco"
  Glen Evelyn likes to modify guitars on his days off. Favoring short-scale Duo-Sonics and Musicmasters, he's crafted several bodies out of teak wood and then bolted vintage '50s and '60s MM/DS necks (plus a '90s Mexican-made DS neck) to them. Pretty high-quality workmanship for a "hobby"!
  Owned by Glen Evelyn
  
  
• '56 Duo-Sonic with '65 Mustang neck, ugly clear refin
  It was a tight fit, and the neck needed some fret work, but overall the transplant worked astoundingly well. I added a pair of Duncan pickups plus new Schaller tuners, StewMac's angled replacement Tele bridge saddles, and new electronics to make it complete.
  Owned by yours truly.
  
  
• '59 Musicmaster neck/'65 Duo-Sonic body, with angled saddles
  "The body is from 1965 and the neck is from 1959. Both fit perfectly! I refinished the body in a blue between Sonic Blue and Daphnee Blue. The original color was unknown. The nitrocellulosic varnish is not a very good job, but it is thin and it is becoming looking 40 years old!"
  Owned by Fabien Cannarella (from France)
  
  
• '63 Duo-Sonic, mahogany body with 24" scale repro neck:
  front | body, front | back | headstock, front | headstock, back
  Mods include the following:
  Warmoth repro 24" scale neck: "It took a bit of surgery (literally lopping off 3/8" from the base of the heel) to make it function on a student scale instrument."
  Fender Toronado bridge: "It wasn't at all difficult, but I had the assistance of a luthier friend's woodshop. All you need to make something like that work well is a drill press so the bit doesn't wander on you. I tried the angled saddles and it helped some. But that was still an imperfect solution. The angled saddles didn't like living in a pre-'64 bridge assembly."
  Original mahogany body re-refinished in clear lacquer; the headstock was veneered with matching mahogany and given a repro decal. Stunning!
  Replacement hardware: Squier Strat pickups, repro pickguard, and staggered-height Kluson tuning machines
  Source: Skip/sidpiks (eBay)
  
  
• '64 "transition" Duo-Sonic, in white (128 k)
  A Duo-Sonic II 24" scale neck on a Duo-Sonic ("I") body. This couldn't have been original, could it?
  Source: unknown (eBay)
  
  
• '65 Musicmaster with '63 neck, in blue
  I know this one wasn't original; can't really tell what type of bridge that is, though.
  Source: unknown (eBay)
  
  
• '65 Duo-Sonic, refinished in blue with full-scale neck
  Owned by Mike Robinson
  
  
• '60s or '70s Musicmaster bass, refinished in red
  "This was a 60s DuoSonic body and a TINY 22.5" scale '66 Musicmaster neck. I was able to use fairly accurate parts throughout except for the pickups, which are from a late 70s Mustang I believe. I've also got chrome Kluson/Fender reissue tuners in place." Owned by Michael Jetton (from the Czech Republic)
  
  '60s Duo-Sonic, heavily modified
  With third pickup, switch, and Mustang bridge/tailpiece installed.
  Formerly owned by Thurston Moore/Sonic Youth, until it was stolen in 1999