1978 sears drive belt

We recently got this tractor. The guy said it is a 1978. I looked at all the pictures and the closest I could see was model 917.257050 or 60.
I went to sears parts and they said they had a belt, but they could not tell me the size. The one that broke is 5/8" by 841/2". It isthe drive belt not to mower deck. I need help

THE BEST DRIVE BELT I HAVE FOUND FOR SEARS SUBURBANS GT16 OR GT18 WITH A ONAN ENGINE IS ROTARY # 12-7626 83" KEVLAR WRAPPED BELT, NO EXCEPTIONS. ALSO IF YOUR TRACTOR HAS A 16 HP. BRIGGS THE MODEL IS GT16 YOU WILL PROBABLY NEED A ROTARY #12-7627 84" BELT ALSO KEVLAR WRAPPED. I HAD A 16 HP BRIGGS ON A GT16 RUNNING A 83" BELT AND TOOK THE ENGINE OFF & PUT IT ON IN PLACE OF A 18 HP ONANA ON A GT 18 TRACTOR AND HAD TO CHANGE TO A 84" BELT. WHEN MEASURING A BELT ON THE OUT SIDE A 83" BELT WILL MEASURE 84 1/2" USUALLY AN INCH & HALF DIFFERENCE. IF THE BELT IS A LITTLE LONG YOU CAN ADJUST, BUT A LITTLE SHORT AND NO CLUTCH RELEASE. DON'T TRY TO USE A BELT THAT IS NOT WRAPPED. THIS HAS BEEN HASHED A HUNDRED TIMES ON THIS FORUM. ( MY CLUTCH WON'T RELEASE) ALSO IF YOU NEED TO REPLACE YOUR DECK CLUTCH BELT USE ROTARY KEVLAR WRAPPED 12-7547, 104" ALL OF THESE ARE 5/8" WIDTHS. LEARNED ALL THIS THE HARD WAY. THANKS FOR READING THIS FAR. JIMMY IN SOUTH GEORGIA.