Casting numbers

[Yote]

just looked at the sticky on exhaust manifold casting numbers. Apparently my 72 demon 340 has the left manifold for a 318. What is the difference?? Is it anything that I should consider changing?? If so why.
Yote

 

[Treblig]

The 340 manifold has a 2 1/4" outlet while the 318 only has 1 5/8" outlet. There's a very big difference!! In the pic is a 360 manifold that I machined out to 2 1/4" next to a 318 manifold. You could almost put the 318 inside the 340/360 manifold.

Treblig

 

[pishta]

That and the fact that the exhaust ports are larger too. 318's 1.14 X 1.59 as opposed to 340/360's 1.25 X 1.75. Your leaving HP on the table as well as an imbalance in the intake from different bank scavenging.