I'm looking up a new oil pump for my '71 455 engine rebuild, and found a reference to '1st design' with a 5/8' inlet, and '2nd design' with a 3/4" inlet.

I found this on Napa online, and it's the first time I've seen this mentioned. Was there an oil pump change in 1971, or does it even matter? No mention if one is 'high volume' or not. I'd appreciate any insight here, thanks.

 

I imagine 5/8 is stock press-in pickup and 3/4 is aftermarket bolt-on pickup.

But I am not well versed in the OP variations.

HV will have longer gears, that's how they get more volume per revolution.