440 compression ratio

I have a 1968-- 440 That came from a charger(so I was told) it has the original pistons in it and I think the original heads on it. I was also told it was rebuilt about 5000 miles ago and I have no reason to not believe this person. The engine is all together and I did't want to take it apart. My question is how do I tell what the compression ratio is? Do I go by the head/block numbers? What compression ratio would this engine have when it was new?
Thank you for your help
Author: plumberick