I looked at the picture you posted on the other forum; Tom Langdon's modification is on the later 235/261 pump. Not sure if the same can be done on the older pump as you picture. I do see that air could enter the suction side of the pump by way of the relief bore vent. As I understand it, Tom recomends the mod as a cure for engines with noisy hydralic lifters.
Originally Posted by mark50
Hi Will,
I'd also be interested to hear Tom's reasoning on this modification. I was all set to do it and asked the same question over on the Chevy Talk board http://www.chevytalk.org/fusionbb/s...1/hl/oil+pump+modification/fromsearch/1/ and it was agreed that plugging vent was unnecessary. Sealing the pump at the inlet is crucial however. Do let us know what Tom has to say!