Ralph, i'm thinking that making two holes and coming thru the transom adapter plate right below the f/r cable is proably best. BUT if your plate is anything like mine that part of the plate is very difficult to access from the inside, this may end up resulting in you having to remove the adapter to do the install, not fun but probably the only way to do it "right".
This is all assuming you are not in favor of making any new/additional holes in the transom itself. (wich I agree with NOT doing)
