This is how I did several J-105 speedo’s. Cut a section of stringer out. Made a Fiberglass tube, about 5” diameter. Glassed it in. Bored hole, rebated core, filled with epoxy. Taped a stir stick at hull surface. Removed flange from speedo tube. Masked everything, buttered it up with thickened epoxy, and set it in. Next morning, I sanded the outside tube edges flush. Instantly cured tack to tack error!