dude the bike that it came from is a 2stroke (NS400R).
We know that, but like said, you need to fill up 32mm part and mill it out to 28mm, complete length.
Otherwise it's very hard to get them adjusted right. TA-09 use different jets then PWK.
I have had a gocart carb on my scooter (Ibea). Preformed fine and easy to work with, because you do not need to change jets (just turn screws).
With that carb I did 20.1 hp on my old setup (Speed6T), so they work well.
If you want something like a gocart carb, get a proper one like Ibea, JHC, Barioni etc.
And not the walbro / tillitson stuff, that's a waste of money.
The advantage of these (semi) drop stream carbs is that you can create a far shorter inlet, which is good for power on high rpm.
The "rule" is that a longer inlet gives more power on low rpm and a short inlet gives more power on high rpm.
That's why a spacer between the manifold and membrane can sometimes be one big difference.
About the difference between the Mikuni TM28SS and the normal Tm28 is that the 28ss is much easier to set up.
With the TM28, you have to change gastube/needle/and some other stuff to make it work poperly.