I did a lot of research on outboard height location when I rebuilt and changed dimensions on a Grady Seafarer transom. I also replaced a single outboard with twins. A "general rule of thumb" I kept finding was, the cavitation plate should be mounted even with hull bottom directly in front of it, AND, up 1" for every 1' outboard is mounted back from transom. I used this as a basis for my twin mount locations, and after experimenting both up and down from that starting point, found that the starting point worked the best for my application.
