Swapping masts and re-rigging

[Brion Toss]

Hi again,
I think you can get at least in the neighborhood with my book. Supplement with Skene's or Larsson & Eliasson. By definition, a double-spreader mast can be lighter than one with single spreaders. Run those numbers. Note that your round mast, if it is big enough fore-and-aft, will be bigger than needed laterally.
Fair leads,
Brion Toss