I have twin HS2 carbs on mine. I did use the 1275 Spridget exhaust manifold. It was a bit tricky making the pipe bent at the manifold outlet. From there I ran 1 3/4" pipe all of the way back. I'm pleased. The best part is getting rid of that crappy clamp system at the original manifold to pipe connection.
BTW I'm not a fan of headers. I suppose for the ultimate in performance a header is a must. For the street a cast iron manifold is much more reliable.
Here is a link to my journal on another site. You'll have to scroll down a few to find it. Hope that helps.http://www.mgexp.com/journal/geezer
Here's a link on this site. I also tried a Rover Mini exhaust manifold but that presented a challenge. I may still use the Rover Mini manifold when the 1275 goes in the car.viewtopic.php?f=13&t=10987