Tricky, unfortunately you are wrong.
The plenum on the left is a 296 (rev up) the one on the right is the 276 that has been modified with lowering the front runners.
you have only referenced one standard plenum (the 296) with the shorter runners with the modified 276 (Mrev) i.e two completely different parts which doesnt show the modification.
Here is the 276 vs the Mrev
313 engine is completely different Plastic for a start and square runners!