Instead of grinding why don't you just use a spacer under the top gudgeon, washers or a delrin block. ( move the top back ). This way you can play around with rake easily. You can also re-drill the piviot hole.
The spacer might be a good idea, it never occured to me. It would tilt the tiller arms up, though, which might cause a problem.
I don't think the pivot hole can be moved, not enough meat in the casting.
