I think this was what I just did...
The end holes are studs - 1/4-20 in the head, 1/4-28 on the manifold side, with conical steel washers. Center two are standard 1 1/4" 1/4-20 cap screws with no washers, and the other two are longer 2" or 2 1/4" (?) cap screws with conical steel washers.
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