Would this work?

[aerosam]

Hmm, difficult one that.

I think it would work but it would be quite a feat to pull it off. The best way to cut off the flanges would be with a bandsaw, I'm not sure if you could get it round that threaded port in picture 2. Also, you would have to pretty accurately replicate the cut on the second manifold to have any hope of welding it back together without any leaks.

I hope you are handy with a TIG welder or know somebody who is cos that will require some expert welding.

After you have it back together you would need to re-shape the ports as your engine appears to have oval ports and the DCOE manifold has round ones. Is there enough meat there to open them up far enough?

Sorry that all sounds so negative, I'm not trying to talk you out of it, just don't want you to destroy 2 manifolds and then find you are stuck with nothing. Best of luck with it.