Alternative belts.
While my experience is unique (read that as custom SC engine in a none SC chassis) you might find the information helpful.
I removed the pwr steering pump, A.C. compressor and added a 5% Jackshaft pulley, this required me to hand select all the new belts.
If you go on line to the Gates & Gaterback sights you can find a listing of all the belts that are available listed by the number of ribs and length. If you have the part number for the belt that is too long, you only need to see what is available in the next size down. Every part store I have dealt with has allowed me to take a handful of belts with me to try and as long as I have not damage the belt or soiled the packaging, allowed me to return the unused belts. I the case where I removed the power steering pump, I ended up reversing the idler spring by cutting off the stop tab and winding it the other direction and re clocking ( rotating the idler assembly and drilling a new locater pin hole).
In one case, for the crank to jackshaft pulley, a 7 rib pulley was not available so I used a 6 rib pulley. The only problem I have had is when one of the belts stretched and began to slip and replacing it with the next size smaller took care of that problem.
Hope this helps.