I need to replace the belt on the lawn mower but the model number is partially missing. This is a 38" cut and an older moldel probably early 90's. How do I find out what belt I need. Any suggestions

Hi,
The first 2 digits of the model are the deck size. Then the next three define the construction, i.e. hood, frame, etc. An "x" next is a divider before a vendor number if it was made to order by someone (like Home Depot, WalMart, etc.) and possibly by a letter of the alphabet for a revisison. The Date Code is the last digit of the year and the day numerically - like 6147 meaning 1996 147th day.
The belt is a 37x63MA until 1996 and a 37x86MA from 1997 toward. They are less than an inch different in length, shape is different I believe.
Picture attached:
Peace,
Clarke