These motors from a bout 1964 to late 1980's all used the same impeller-----4 and 6 cylinder Mercury also Mercruisers used the same impeller.-----Every good boat shop would have it in stock.----Last 2 numbers in the part number are----84-----Should be easy to find on a list.
You will want to replace the impeller, wearplate and 2 gaskets, as a minimum. Inspect the pump cover for cracks and wear. Inspect the pump base for melting. Replace all damaged components.
