Can I add a shortened comp tip to my old mast to do this? Anyone have one for sale reasonably? Other options?
The cut off Comptip would work well, but you might be better off just sleeving an "extention" section on to the mast. The top part of the mast is under the least amount of stress, providing you don't have a backstay, a masthead rig (jib goes all the way to the top of the mast) or a spinnaker halyard mounted about the join.
I've got the top part of my 14's mast (cut off for the Comptip) that I'd send you a piece of for a reasonable price. PM me.