Long vs. short distributor oil pump drive

SoCalCruising

Founding Member
Jul 25, 2000
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As some you will remember, I built a 331 using all new parts. When ordering the distributor, I was asked if I needed a long or short oil pump drive on the distributor. I didn't know that there was such a distinction. Can anyone tell me precisely what it is about a motor combo that would require one or the other?

Since the long drive would not seat onto the block (drive too long), I am using the short drive, I just want to understand the difference. Thanks.