there's a much easier,and better way to go about installing a transducer in that fashion you described...however,i choose to go an accepted route,use the proper equipment for the job...it's kinda like using a volvo outdrive behind a merc engine,something i wouldn't do...if you're gonna install something,use the proper equipment,granted,sometimes the improper equipment will work...
honda motor company had a print ad a few years ago,it was a picture of a chair,one leg was broken,someone tied a stick to it,this was the repair,it stated " sure it's fixed,but would you sit on it "??? me,i stick with what works for me,i'm sure you can spend your time "reinventing the wheel",i'm pretty confident you've got time on your hands with the financial market being what it is...it's much better to use the correct thru hull ducer,along with a fairing block cut at the correct angle,or to properly install a transom mounted 'ducer-afterall,that's what they were designed for...

and no offense,if that's the best set up you can come up with,i see why you're in the mortgage buisness rather than the engineering buisness...