I have always made it a rule to replace the oil pump if I had the engine apart. That said:

From the parts interchange manual you are looking for the grommet, pump suction pipe, p/n 3835868
http://chevy.oldcarmanualproject.com/parts/1929_54/132.htm

Obsolete Chevy parts shows this part
http://www.parts123.com/parts123/yb.dll?parta~partsort~1~cadeflkx
Do not order via the computer. Call 1-800-248-8785 to be certain you get the correct part.

Fred
52 3600
69 C-10