I have only looked at a maybe a half dozen 10EE that were not seriously molested in past life, but I know they take an A belt, if you have doubts call Monarch. That said if the belt rides in the groove without bottoming out and does not shred and make a mess its probably okay. I am sure on my 56 the belt rides a bit high in the groove but that is okay compared to the opposite. Even though the lathes came with either a 3 or 5 hp motor I serously doubt most folks use more than 1 hp so if the belts work okay, don't shred and allow you to do the work you want to do I would not worry about it. I am not up on the later machines but a 70s machine still had A belts as far as I know.