IC coupler sizes?

[scojack_2001]

I need to replace the IC couplers on my GN. Going to a Dutt neck anyway. One of my current ones is a little beat from the up-pipe coming off so many times...

I know I need a 2" to 2.5" step-up for the Dutt neck, but what about the up-pipe? 2.5"? 2.675"?

I can find new couplers and clamps locally, which is a good thing.

Any help appreciated.