I just found out that in 79, the 460 went from internal balance to external, so I'm a little embarassed to say I installed a flexplate from a 460 of unknown year. I don't want to fire up the motor and find out I have the wrong one. Is it possible to identify the flexplate through the front cover, or do I have to pull the tranny?

 

if it has a counter weight on it it is late model. ie:externally balanced.

 

Thanks for the response.
I know about the weights, but will I be able to see them without pulling the tranny?

 

I think you might be able to see them through the inspection cover - or at least you might see the spot welds if the weight is installed on the tranny side of the flexplate. For maximum effect, the weights are out by the ring gear - this is the area you can see through the cover.