I don't know about the tranny but it shouldn't be a problem atall. I had a hitch on my bumper for a few years so I could tow a jet ski and I had a friend in college that had a 83 mustang vert that he used to tow a jet ski with, his was a manual, like yours. What is it with convertibles and jet skis?
Only bad thing about a GT is that you have to cut a hole in the middle of your plastic.
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Rick
My 89lx(updated 2/21/2001)
My 97 Cobra