Jim,
With regards ST G60 Blue Head, I do have a small collection of these engines and they all have the 9mm choke. Smaller chokes were certainly produced but I think it was on the much earlier models that did not have the 'mag' type carb. One of the pictures I have posted shows the most recent muffler produced by ST and it will fit the G60. I must admit it is not the prettiest of mufflers but works very well provided you do not push the muffler fully home, if you do the peak RPM will drop by about 2000. For those of you who have a keen eye you will notice that one of the G60's has the 'present day carb,' the motor is a bit a a hybrid, it was made for me by the UK ST agent and enjoys PDP porting and ABC construction. This PDP/ABC engine was quite a rarity in the UK, I believe only about 10 were ever imported, how about the USA?
They are great engines and they are still sitting in boxes out there somewhere in peoples attics!
John