I do know the needle is set different on the KOSO than the Keihin.
The needle should be set at the 2nd notch from the bottom where your Keihin should be 2nd notch from top. But your jetting is up to your builder who should of told you where to go on the jetting. Your elevation and humidity will change from state to state. This is all I can help you with.
Yes you have to have a 28 to 30mm boot type like the koso. I don't know what kind intake your running but you may be able to buy the fittment for the 30 to fit your intake call Snyders in the morning Shawns a good ol boy he will help ya out.
I'll have to get back to you next week. I bought this carb. from Marc (Hot Quads), and he is at the Nationals racing this weekend. Honestly Marc has never run one of these, so i am treading new ground for him. I want to see what other options he has for me... he was out of the 28mm powerjet stage 6 carbs, otherwise that is what I was going to buy.