the 583 rotax motors are bulletproof. It is liquid cooled as well and should top out over 90 in good conditions. It was one of the best snowmobile engines made actually. It made decent power too with the rave valves. I drove a formula 583 and was impressed with the engine especially for being older (1998). The 583 rotaxs are like ski-doo's version of polaris' 488 fuji twin.
2003 pro-x 700;
TracksUSA 144" tip-up rail extensions
1.25 camoplast predator /120 1.40' extreme max SS studs
VanAmburg tunnel extension
SLP Powder-Pro skis, Powder-Coated suspension
Holtzman tempaflow-420 main jets
10-64g weights w/ round almond spring
24/42 gearing, gutted airbox, PERC, torque arm