Are you running the original short waterpump and brackets or a long waterpump and brackets? With the long all that is required is a short piece of tubing to act as a spacer to take up the thickness of the stock manifold. I do not remember what is needed with the short pump, but I would think it would be a similar situation. If not aftermarket adapter brackets should be available.
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70 chevelle ss396 conv
66 chevelle ss396 hdp/conv
55 chevy prostreet