What have I got here? Magnum 5.9 Flex plate identification

Heyah, guys.

Sorry for the crappy pic...this is the "disk with the bite taken out" style flex plate, approximately 12" in diameter....

Basically, I'm hoping for some more guidence as I prepare to install my Magnum 5.9 crate engine that I bought used from another forum member along with my 904.

Question 1:
A far as I know, this is the original part. The engine was previously run with this flex plate...but is this flex plate too big for use with a 904? I can't find the correct measurements anywhere!

Question 2:
If it is the wrong plate for use with the 904, I understand that a stock Magnum flex plate can be used...but that there are different types (weighted versus non weighted) based on the year of the Magnum. Based on what this engine came with, can you tell which I would need?
Thanks a million for any help..

It seems that the stock Magnum flex plates are available from Rockauto, etc...

Thanks yet again!
-Mike