|CT90 USE CONVERSATION*|
The 2.50/17 Gazelles will work just fine front and rear for your CT90K2. Like Mel mentioned, the 2.50/17 will look a little narrow out back, but other then that minor aesthetic issue, it will work great.
I put 750 happy, trouble-free miles on a set of 2.50/17 Gazelles with my '67 CT90K0 and the narrower width of the rear tire never bothered me a bit.
In my humble opinion, the Gazelles are a much better choice for the street then trials-type tires, and worked great for gravel, dirt and rock roads up and around Mt. Rainer. They also worked very well for me on the ice and in 3"-6" of snow.
No tire is perfect, and no tire does it all, but the Gazelle is a pretty dang good all 'rounder.