Quote Originally Posted by shoprat
The 428 has a added weight on the harmonic balancer also (external balance)

Ron
That's the SCJ only. It used the "cookie cutter" crank spacer to put the missing crank weight pad on the nose to balance the heavier LeMans rods. It also used a larger dia and thicker harmonic balancer from the 427. If you put a CJ and SCJ crank side by side you'll see the CJ unit has a extra weight on the cranks 7th counterweight. The SCJ does not. Also the CJ and SCJ flywheels have different weight pads but as mentioned both and the std 428 are all external balance. The CJ and std 428's used a FE stock balancer with another exception. The 428 PI's I believe used the larger dia 427/SCJ harmonic balancers. But it's been a few years and the mind ain't what it used to be. LOL. I'm pretty sure my old 67 Shel had one tho...

I'll agree with everyones train of thought....if the 390 is a good running engine enjoy it and leave well enough alone. The 66 bird is a wonderful ride so enjoy. If a 428 is what you must have you can shop and build a shortblock and change it in the future. It's next to impossible as mentioned to tell a 428 from a 390 from the outside anyway. But that is your decision.

G.