I am trying to find the size belt I need for a 1968 Murray 12 hp I/C 12ic/36 model #8-36568. Old belt is not available & no one around here can seem to help me. Any help would be greatly appreciated.:)

Hi,
One place in particular has old manuals:
K&T Parts House Lawn Mower Parts and Chain Saw & Trimmer Parts
And another crosses the belts, some do not cross to even lengths:
Outdoor Power Equipment Information
Peace,
Clarke
PS Tell me if you do not find; thought you might like to see where I would look!