Two on the exhaust manifold? I seem to recall there should only be one there - near the collector. The other one should be just aft of the catalytic convertor.
Typically, an inline engine will only have one in the exhaust manifold - if you've got a "V" engine (V6, V8) you'll have one in EACH manifold, and then one after EACH catalytic converter (one if there's one, two if there's two,) but there's not reason for you to have more than two. You may want to have another look to be sure. Also, if you have some sort of aftermarket fuel/air ratio gage installed, that could account for the extra in the manifold...
5-90