difference between 912/914/915 block cases

I have searched the forums and internet fairly well and haven't found the information im seeking.  I would like to know the differenced between the newer cases/block that changed in what appears to be 2006 or possibly 2008.  Also how can someone identify if this the engine is indeed a later model stronger/beefer case?    Is there some sure fire way of seeing a big difference between the two?      On this same note, where are you guys sourcing parts at here in the US for best pricing and service.

Thank you in advance!

Mike