[JJ88]

Hello,
I have a 1964 Pontiac Grand Prix with a 389. The car was sold to me 24 years ago as a 421. Pulled the engine to seal it up and this when we discovered it was a 389 and not a 421. We put all new bearings, cam, lifters in the motor.

Parts were ordered thinking it was a 421. We were told no problem as the parts were interchangeable for what we had ordered. My mechanic noticed the stock cam had two holes drilled in journals 2 and 4. The new cam did not have these holes. Apparently this was a 1964 thing that Pontiac did.

When we started the engine not much oil was coming up into the rockers. This is when we found out that the new cam was not for a 64 but for a 65/66. The difference is that in the 65/66 they had hollow rods with an oil holes in the rockers. The stock 64 rockers have no holes.

The question I have is could we upgrade the rods and rockers to the 65/66 rocker and leave the new cam in our should I go back to the original cam with drilled journals? Ironically the engine does have hollow rods already.

Asking because obviously trying to save some time and money as changing the rockers and rods is a pretty quick fix vs new cam.

And thoughts would be greatly appreciated. Thanks,