Bits,
Sorry to hear about your mishap
But a Big Congrats on the recovery
If you have the means to custom build you own bracket, I believe you can use your 20" motor.
Look at my setup with 25" motor. That is an aluminum B-Bracket(26" set back) that I later added the larger floatation chamber. The motor is mounted on the last hole as high as possible, and still could go alittle higher. The waterline is 1" below the black boot stripe. Notice how high the swimplatform is out of the water, with a shorter shaft motor, that can be lowered 2-3"
What ever you do with a bracket, just remember three things...FLOATATION,FLOATATION,FLOATATION!
Lloyd