Are you trying to use this one CSi transducer for high-speed depth readings?
If so, then I think that you will have to install it just to the right of the rightmost drain hole/outlet. This of course will expose it to possible damage from stumps rocks and the like.
Instead I recommend that you install it just to the right of the motor mount (up on the transom, not the step) and install an XP-9-20 inside-the-hull DualBeam transducer and an AS-Si-DB-Y cable to connect both to your 798ci Si unit. This will help protect the CSi transducer and give the best possible high-speed depth readings.