Hey..Thanks Todd I have had that problem..
ops:
I kept replacing the pumps with the older thicker casting pumps and even a BBC HV oil pump it help up until the crankshaft twisted in Half.
I believe what was happening was the crankshaft was cracked and causing a vibration in the motor.. It was a Cast steel crankshaft.
Since then I have swapped to their recommended pump..
http://data.melling.com/Select/small_block_chevy.php
And upgraded to a 4340 crankshaft. I think I put the cast one thru more than it's share of abuse and it failed it breaking off the oil pump was a sign and I didn't want to think that. If it was mine I would have the crankshaft magged and get one of these pumps. I use the 10552's.