Before drilling any holes, get uner the boat and insert the cb into its slot and adjust it forward and back so that there is about equal space at either end. Prop it up with wedges, so that the cb is in the up position. I can show you pictures of how to prop it up on your trailer with a 2x4 and small wedges, and a couple of c clamps. If you wish, send me you e-mail to roger02 at mb dot sympatico dot ca replacing the at with @ and the dot with .
After the cb is in place climb into the boat, reach into the inspecton ports feeling for the holes about 8" forward of the ports, and with a pencil mark through the cb trunk holes where they open up to the cb. Mark both sides.
Remove the cb from the slot and measure your marks, then drill. I do think your discription is accurate, but this method will confirm those measurements. Don't forget to re-gelcoat the inside of the hole you drill so that water does not get into the laminate if it is exposed. Check your bolt to make sure it is a good fit and does not bind in the hole.
To check the workings on dryland, careen your daysailer and work the cb.
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