I have 3 at1 hooker headers and I want to use one of them on my 71 at1 but the flange is different and the pipe doesn’t fit in the flange.  Does anyone know what flange I need?  Obviously finding a hooker one is impossible but I didn’t know if the trick back then was to use a flange off a different Yamaha like a dt1 that made it work.  If not I can prob have something made but that would be a final option.

thanks
 

I just traded off a Hooker header for a stock pipe on my CT1. Here is a pic of the flange that was on my bike.