I don't know if this will be of use but I have a couple of A&I belt numbers. I needed the pto drive belt for my MF12G with the Predator engine conversion as I had been running one an inch to long and it slipped now and then mowing. All I found locally at a reasonable price were in 2" even numbered increments. This conversion uses a 31" belt best. 30" belt would not let the cutting deck disengage. I also needed the pto to deck drive 50" belt so I ordered both from V-Belt supply in Sioux Falls, SD. $22 shipped for both belts.
13 HP Predator engine conversion PTO drive belt #A29K, 31" belt.
PTO to mower deck drive belt #A48K, 50" belt that fits 1975 MF12G