I bought recently a pair of 1 1/4 " SU carbs from a Triumph Spitfire. They came with the manifold, and my plan was to modify the manifold like Mike made it. I found that is easier than i thought and the holes almost match. Here`s a scan of the intake and you can see where is needer to port or have some held job.
I made both round and oval examples.

I think is not necessary to cut between the two.