Well, technically, they should fit in there but are not what Mikuni intended to be used. As I said, I think the large head style was chosen for it's better ability to hold the needle jet in place. The head is bigger so will have more and better bearing against the washer. This should make it less prone to coming loose. If you remove that washer, you can see the needle jet below it. This is what the washer and main jet hold in place. They pull it down tight into the carb body and hold it there .....
Usual setting for BS34 mix screws is 3 to 3.5 turns out. A larger pilot may allow slightly less than that, but maybe not. I would start them at 3 turns out and fine tune from there.
Usual setting for BS34 mix screws is 3 to 3.5 turns out. A larger pilot may allow slightly less than that, but maybe not. I would start them at 3 turns out and fine tune from there.