Good call, as mines a track only bike, I'm not hamstrung by pump gas. I always thought the 626 was a 26mm, but certainly those available for the rocket 3 and T150 are 27mm.
Personally I like fitting chokes to my road bikes.
If you are planning to twin carb it you will need to sort out some manifolds and ideally rubber mounting to isolate vibration and heat away from the carbs.
Nothing wrong with a single carb, mind you. Chris Vincent only ever ran single carbs on his A10 outfits.