99 sport track update

have a 99 sport (440) with a 121 track. I have a 121x 15x 1.5 polaris track pn 5410946 that i want to install in this sled wondering what mods i need to do to make it fit in reference to track clearance. any help would be greatly appreciated.

the factory track is a 3/4 block (storm track) I was wondering on advice as to what driver size i should use. (has 9t) and if i should drop down one hole in the front suspension mounting. I am already planing on dropping the rear with some stock brackets off of a older xlt. was also wondering about gearing to off set the smaller driver and 1.5 track. this sled has a 60 over 440 in it and will be primarly riden by my kids 10 and up.