I am replacing the oil pump on my Slant Six (1974). I was able to locate a NOS oil pump from a dealer here in Calif. The NOS has 5 holes whereas the original pump 6 holes. I have read it is okay to use the 5 hole pump without any trouble. Comments appreciated...

I think Doc was trying to put together a list of the years/vehicles that got the six hole pump vs the 5 hole pump. My '87 truck's original pump had 5, the hi-vol pump I ordered from the dealership only had 5 holes drilled, but there was a bung to drill a 6th. My block only has provisions for 5 holes.

At any rate, you will be fine using the 5-hole pump. ( I believe the sixth was eliminated because it was determined to not be necessary)

-S/6

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The "Silver Bullet"
87 Ram D150

The 6 hole pump seems to have ended around '76 or so. The 5 hole pumps have a thicker rotor in them.

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Official Cookie and Mater Tormentor.

Rotor thickness is related to the number of holes,
6 hole pumps have the 5/8 thick rotor, 5 hole pumps have the thicker 7/8 rotor.
Either one works fine as long as the gear holds-up.
DD