Bought new skid rails for a 91 Indy 500 Classic and got them home and noticed they are about 6 inches longer at the back then the old ones. The Polaris parts look-up says they are the correct rails and they match up hole for hole until the back end of the rail. There is another rail listed but when you look at usage it is listed for newer snowmobiles. The part numbers I got where 1540615 and 1540616. The alternate numbers are 1540553 and 1540554. Also what are the part numbers for the HD torsion springs for this snowmobile? I got part numbers 704126-067 and 7041247-067 and they look like a smaller diameter spring than the originals.