I have an old PowerMatic planer, circa 1964, whose knives are being re-sharpened and in the meantime I am inspecting the drive belts. I found one that is very worn and cracked so I removed it and measured its length by wrapping a flexible tape around the outside and got a length of 63.5 +- 0.125" based on several measurements . The manual is no help in describing the belts so should I replace it with a 63" belt? I know a belt will stretch/wear so is 1/2" undersize sufficient or should I go to 62". There is no way to adjust the sheaves to get proper tension.