5713 does not look right for a machine made by Geo Monro, it could be a machine made by another maker. Can you check the makers plate or better still post a picture of it.
The manifold is prone to damage, either in use or when trying to remove the exhaust from the manifold, I dont think I have one in my stock of secondhand parts, the 35 is not so common as the 56 in the UK.