I looked at a couple suppliers and both only list a single mainspring P/N and Barrel Assembly P/N. Honestly, the only thing I could see is what ETA did with the C07 movements where they lengthened the spring and reduced the arbor diameter. But then none of the C07 parts show up in the commercial suppliers websites; you have to have a Swatch account and order them directly from Swatch.
A more likely mod would be to reduce the rate to 21600 with a heavier balance wheel and a 15 tooth escape wheel. That's a 25% improvement which would get you to 60 hours. Still, those parts wouldn't show up on the commercial suppliers websites either.
Just bite the bullet and get a Speedmaster '57.
