Join Date: Jun 2005
Location: New Orleans
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before you go to the trouble (and structural risk?) of moving the mast step, try reducing the mast rake. You said it's raked quite a bit, so ease off on the backstay, take up on the headstay, and see if that changes the balance and gives you less weather helm.
One other thought. How big is your jib? Maybe if you got a slightly larger one with roughly the same hoist measurement, you could pull the center of effort (of sails) forward a little. You'd still have to move the jibsheet leads, though maybe not. If you could borrow such a jib, you could find out the answer for free.
Weather or lee helm is dependent on where the center of sail effort (CE) is in comparison to the hull's center of lateral resistance (CLR), or pivot-point. When both sails are trimmed properly upwind, you want a slight weather helm.