If you have to buy them then use plain v belts as they are a lot cheaper
Do not run them for long enough to get hot because when they get hot they get stickly
So slip one on try the blades on-off-on-off a few times watching for the blades not fully stopping or belt burning on the engine pulley
You will need to bypass the seat switch to do this or need a helper .
When you find the size that works best use the "belts by length " tables to see what OEM kevlar belt is the closest to the size that works
Also check the blade brakes can actually stop the pulleys turning
In particularly the one on the right side ( push side ) of the engine pulley as this is the one that causes the deck belt to go slack around the engine pulley
I had an MTD Black that drove me mad for years as it burned belts left right & centre tilI twigged the left brake worked well but the right did not
So the left pulley stops turning which causes the left run to the engine to go tight while the right was loose so the belt burned