I'd put it on the SB side to the RHS of the elephants trunk centred below the flat part of the chine rail if that makes sense.
I've the same unit and done this on my RC 585 which appears to have similar hull to yours (without elephants trunk) works fine.
May I add that I simply stuck my transducers on with 3M VHB sticky pads - I have 3 transducers - Lowrance, Raymarine and Garmin all within a few inches of each other.
I was told I would get loads of interference and none of them would function properly, also I didn't want to drill loads of holes in my transom whilst trying to find optimum position.
I cleaned the transom with Acetone, lightly abraded the transducer mounting surfaces with wet and dry then acetone to remove any grease or slime, then stuck them on with the VHB pads. Bearing in mind the transucers are very large - especially the Raymarine one and the rib has been at sea (airbourne) in very rough conditions, and deliberately been run onto sandy beaches etc amazingly after 600 miles all 3 transducers are still solid and sticky pads are holding.
I don't get any interference and amazingly all 3 worked perfectly in most conditions from the start so no need to change positions.
If you do need to move them just warm up the sticky pad by pouring boiling water over it and they peel off leaving no residue or damage to the transom.
Sorry dont have any pics