What is the difference between a production engine and a Mopar Performance crate hemi?

The reason I ask is LQK has tons of low milage hemi engines for 1/3 the cost of the crate engine. If there is something different could it be changed?

Thanks for your help in advance.
67 Coronet, 68 Roadrunner, 69 Super Bee, 69 Coronet 500 convertible, This Space to be Filled, 79 D150 360, and a severe case of Mopar a,d,d