Magnum flex plate 904 vs 727: identification?

So my 904 is ready to be picked up and installed on my Magnum crate engine.

The engine came with the flex plate but It just occurred to me that it might not be compatible with my 904 and that this might be a problem since I believe I heard that the 904/magnum flex plate is no longer available :banghead:

How can I tell? The plate is about 12" in diameter...