I would use them if possible. Sometimes it is impossible to use any. If you can use one on each side under the pan, do it. If you can use two, then do it. If you can use none, try to use some good gasket sealer (not silicone-it breaks down when gas gets to it) on both sides.
As said above...dummy it up with two on each side and see if you can start bolts on both sides...
If not, remove the top one and try again...if the bolts start, do it that way
If not possible, remove them both.
