Just stock stuff? I got stuff from my 87 and an 89......
That would work - if you also give him item 21 in the dwg. From 87 up (86 for CK3 series), the front bracket became...like a full face design, which utilized three mounting points. That is probably what came with your 87/89 350 M's.
Previously, just two bolts were used to secure the pump/bracket - the pivot bolt and one (upper) adjusting bolt. The full face bracket had another hole for a lower adjusting bolt - and that "S" shaped brace (21) was required if that lower bolt was going to be used:
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Thing is, if the P/S pump mounted fine using just two bolts up till that point, it may well be that the lower one isn't really critical.