All harmonic balancers, regardless of year of the 429/460, are neutral balance pieces and will fit any 429/460 engine. The difference between internal balanced/external balanced rotating assemblies is in the crank spacer (located between balancer and timing cover) and the flexplate (bolted to rear of crankshaft).
Quote Originally Posted by lightning1901

here is the info i have on parts i can see, i cant actually get a true date, only casting numbers,,

Block D1VE A2B
Heads D3VE A2A
Intake D6VE 9425 A3A
Water Pump D2VE BA
99% likelihood that your engine is internally balanced. All of the D1VE blocks came this way from the factory, but it is technically still possible that somebody rebuilt your engine and fit it with a late model exernal balance crank..although this is highly unlikely.

Paul