I use the Liebert VT belts on everything I can, they are a low stretch, low dust belt and are matched sets. They are made by browning for Liebert units. I can't say enough about these things. Also I recommend (if you have not already) get rid of any variable pitch pulleys and any that have grooves starting, they're just a belt grinder. Put in fixed pitch and put the time in to align the pulleys right. That also means that you may have to shim the backside of the motor to compensate for the pull of the belts. You know you did it right when you come back on the next maintenance and the paint has not worn off the pulleys yet.
If you have any questions you can e mail me and I can send you some VP to fixed pitch conversion paperwork.
do things right the first time is cheaper.