Try the new Hobie plug/cassette, it is much sturdier and the locking nubs on the sides are much stronger...also...there's no need to hack up the motor..the Motor Guide R-3 fits right through the mirage drive hole. I run the cable thru the boat and use the minnkotta flushmount three-prong twist-plug for the power, rigged by the mast mount up front...nice and clean rig.
I also use a larger battery mounted behind the seat which still allows for the bait tank to fit and a longer run time. I have the same small PWC battery that you have and I use it for my Scotty power hauler... but it really doesn't give me very much run time with the trolling motor. The R-3 is only about $125. I take my mirage drive with me as backup but haven't had to use it yet.
Before I started the project I went to the "Trolling Motor Doctor" in Long Beach and we tried all his smaller (affordable) motors untill we found a good one that fit in the mirage drive hole. The R-3 with the 2 blade prop fit best. He was quite helpful and really knew all the motors very well. Since I'm on the Hobie team I tried to stay away from the Johnson products (Minn Kota).