My buddy Dale loved the S&S "L" carb, I assume it has good response since the float is to the side of the venturi, S&S sure makes carbs that will suck a lot of air.
Man, maybe one day I will try to bump start my 1962. It has the dry clutch so it can get up to speed while in gear. It never occurred to me you have to push the bike backwards to get it far from the compression stroke. I learned pushing a bike with a buddy on it, the secret is to not stop pushing when he dumps the clutch. Being in a higher gear might help as well.
My hats off to you, its good to hear about the round-slide Mikuni from a guy that really ran them, as opposed to a "friend of a friend of a guy that he knew."