a Body / swap to b body.

Let me start over.
I have a fresh built 225 / that came out of a 65 date code a body.
I am going to pull the 225 / out of my 64 b body and put the engine that came out of the a body.
I am going to use the b body mounts and put them on the a 225 engine.
If the engines are exactly the same configuration, why would the size of a body and b body K make any difference?