OEM...the Camoplast Series IV tracks are one of the BEST mountain tracks ever made. The 2", 2 1/4" and 2.4" lugs are true climbers...all are 2.52" pitch.
if you start swapping out to 3" pitch tracks (or 2.86") from newer sleds, you will start running into track vs cooler/tunnel clearance issues and w/o doing a drop and roll, you will have lots of issues.
I have 4 of these sleds now...and another complete sled in boxes...I have 3 166 tracks, and 2 159 tracks...LOVE THEM!!!!!!!