The trick with this particular aftermarket seat was mounting it. I had to get really creative to use both the stock hinge and stock seat locking mechanism. In the end I made it work using plastic spacers. Between the frame rails and the seat I used silicon stoppers from my local home brewing store. These were screwed in from the top of the seat with flush self tapping screws. Weird I know, but they worked out beautifully. Can't see them when the seat is down and will be covered by the seat cushion.
I also want to be able to squeeze my wife on the back when we scoot around town. So I needed to brace up the rear of the seat to avoid potentially cracking the fiberglass. This also required some thinking, more thinking, and beer. Ultimately, I used hard plastic stoppers (again my beer store folks had them) bolted to the C frame in the back, with interlocking plastic stoppers attached to the seat with screws. This way the rear of the seat cannot be compressed down, or to either side. When the seat is down, the rear of the seat is locked in.