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It should be a normal bolt. You can measure yours to be sure but the one block I have here is 7/16 x 14 thread size. Some applications use the little spacer and some do not.
Bill is correct. That is UNC coarse thread 7/16"-14. All 1971 Oldsmobiles except the Toronado use the thick spacer in Bill's photo. If you omit the spacer, the PS pulley will not line up. On the Toronado the differential bracket replaces the spacer.