Jerry has the engine ID facts for you. If you do have the Continental engine, there are two types of new manifolds available. The most commonly found (and cheaper) is the type used on Ferguson 35s with the Z134 Continental engine but they work fine on the older TE20/TO20/TO30 Fergusons. They look different but the only main functional difference is where the exhaust pipe attaches to the manifold. The original manifold has a beveled flange and clamp where the pipe attached, whereas the later/replacemnt manifold and pipe has a three bolt flange with a gasket. Many times the new manifold will come with an adapter to allow use of the older style pipe connection. If you need a new muffler pipe assembly anyway and you get the newer style replacement manifold you can buy a Ferguson TO 35 muffler which will bolt up directly to the new style manifold and eliminate the need for the adapter.
There is also a new replacement manifold that looks like the older style manifolds if originality is important to you. They tend to cost a bit more however.