blk96gt...
The 100 and the 125 share the same bolt pattern so it will physically bolt up to the mount just fine. I think the 125 is 1/2" longer or so. You may have to adjust the cowl a bit. But, it will fit the Showtime just fine and you'll love the extra horsepower. The 125 is a much better fit performance wise than the 100. A APC 16x6 or 17x4W is the prop. Mine pulls the 17x4W a little bit better.

Thanks
Barry