On all Ford built engines besides the casting dates of the components, there is an assembly date hand stamped into one of the casting ears on the front of the block.
Usually, that is about a week to ten days after the casting date on the block. On US built cars the build date would be about a week after the block is assembled.
I'm not sure if this subject was ever discussed in relation to Panteras but keep in mind the engines were shipped the cheapest way to Italy. Now the block was cast at the Cleveland foundry but I don't know if it was assembled there or where the assembly plant actually was.
The cheapest way would have been by boat and you would have to allow for the time to get from the assembly plant to the port of departure.
A month time in between might be on the tight side? Six weeks maybe?
Then who says that they were installed into the Panteras by the oldest first? Probably just the ones in the front of the pile went in first?