I had the internals balanced at the machine shop and thought my flywheel (pontiac)was neutral balanced. Thinking neutral balance does not affect the internals. I also ordered the front crank balancer from butler. Wonder where the balance stands there? I believe the machine shop took a reading on the flywheel before and a shim (I am guessing now) brings it back to where it was?? They told me they have no specs on something this old. I showed the beveled edge because someone on another post commented how it was close to its max mill by looking at that edge.
Hmmm. I am definitely not an expert on this and know that peoples comments can insite fear into any engine build as we want to get it right and not have any major disaster.
OK, further research on Pontiac harmonic balancers say you should be OK with the engine internals balanced as an assembly and then going with a neutral balance flywheel. The harmonic balancer according to a Hot Rod article states,
"For many other makes, the hub contains a slight imbalance that is used to finely balance the entire reciprocating assembly, hence the name harmonic balancer. That isn’t always the case with the Pontiac V-8,
however. Besides original 265/301 units, Pontiac hubs were neutral balanced, serving no balancing purpose.
Vintage Pontiac literature refers to it as a harmonic damper, and for the sake of accuracy in this article, we’ll refer to it as such. Be sure the aftermarket damper you’re considering for your Pontiac is internally balanced."
That said, you can go with a neutral balance flywheel. I do not know if the factory flywheel is neutral balanced to match the neutral balance harmonic damper, but assume it to be based on the article. I know in my past, with factory engines, it was no problem to slap a different Pontiac factory flywheel from one engine to another or swap from an automatic to a 4-speed.
It may be when we rebuild our engines and use other than factory parts that the damper/flywheel/flex plate can be used in the balance of the engine. It may simply be a cost effective measure to do it this way as when you balance an engine internally, it may require adding/welding a heavy metal called "mallory" onto the crankshaft and from my understanding can be costly depending on how out of balance the assembly is. My machinist subs out his balancing to a shop that specializes in this and the engines I have had him balance, he always includes the harmonic balancer and flywheel/flex plate as part of that process.
So, what it appears you want is to have a neutral balance flywheel. I do not know what the minimum thickness is of a flywheel before it cannot be resurfaced any more. I really am not a fan of cast iron flywheels for a HP engine if you can avoid it. Certainly the factory had no issues using them. A steel flywheel is of course an added expense and like most, we all have budgets.
Going with an aftermarket steel flywheel can be a better choice and you can go with a larger clutch set-up. Most are drilled for both the 10 1/2" disc and 11" disc. The more disc surface area you can fit, the more the clutch will grip. I have the Hays steel flywheel, neutral balanced. I am actually using a McLeod 12" set-up which bolts up to the bolt holes for an 11" clutch assembly. Single disc, but more surface area to really grab. First time using this, so hopefully it will work great.
You might still want to drop the flywheel off with your machine shop and let them check it for neutral balance - just for piece of mind and so you can sleep at night.
From my experience, when you rebuild an engine and as you hit the road with it, you become extremely sensitive to EVERY little vibration, whir, change in pitch, creek, and any other noise you hear or even imagine coming from under the hood. Seems you don't have quite these concerns when you buy a car and run the engine that already has miles on it - you just shrug it off and figure if its going to blow up, then let it. Not so with that new engine build.
So I would drop off the flywheel just for that reason alone.
Don't know if you are a Clint Eastwood fan, but it is just like the movie Dirty Harry when he has the criminal under the barrel of his .357 and attempts to reason with the criminal as to whether he fired 5 shots or 6 because in all the confusion, he had forgotten. With the barrel of that big gun staring the criminal in the face, the criminal gives up the fight. But after he does, he looks at Clint Eastwood and says, " I just gotta know." Clint pulls the trigger and the gun goes click.