This could be a fun project. I assume your frame is aluminum (I love that frame by the way) so another cruiser frame won't save much if any weight. Are the stem and fork on this bike steel or aluminum? If they are steel you have the potential to shave another pound or two off by going aluminum. Carbon forks with 1 inch threaded steer tubes aren't plentiful but you can find them. These changes along with the mods already discussed could get you close to your goal.
Keep us posted. This will be an interesting thread to follow.
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Don