What is needed to adapt this to a US spec FD. I heard that it doesn't bolt right up, is this true? Why? and how do you make it work? I heard that it is larger.

Larger UIM ports
Larger elbow
not sure if the trottle body is larger

 

You need the cosmo 13b LIM, UIM and a 20b throttle body. All the runners are the same size...unlike the the US manifolds which have smaller center runners.

Also you can't just adapt the Cosmo upper to the US lower, it's way off.

Btw, I have a Cosmo 13b UIM if your interested...