I should explain my original post a little better. It certainly was not by intention to cause anyone concern.
The reason I said "technically" was by the correct definition, a true internally balanced engine is a neutral balanced engine using no external components to correct an imbalance.
Because a factory Pontiac engine used the flexplate to correct the imbalance, it is by correct definition an externally balanced engine.
However, because all normal factory Pontiacs (sorry 301 guys) where internally balanced to a specified spec vs. most other manufactures, it is generally referred to as internally balanced. Don’t quote me, but I believe the unbalance was 7 or 8 in-oz. (1 ounce of unbalance at a 1-inch radius). All factory flexplates were then manufactured to offset this.
A balanced engine is a balanced engine. Makes no difference how it got there. For high performance engines, a neutrally balanced is usually preferred because most of the aftermarket components are neutral balanced. (Although a true race high RPM engine should still have all components checked.)
Any reputable engine builder should certainly know what they are doing, or they would not be in business very long. My pet peeve on this subject is when shops modify the flexplate to balance the engine without informing the customer that they have to keep the componts together to keep it in balance. (Exception is when a shop modifies the factory flexplate to neutral balance it)
