...I have been watching this thread with interest as I have a MC28 with a tuned 300 kit on it as well, although I have yet to set to work on it so cant really offer an advice as I have no experience. It currently has RS carbs but as its going to be a road bike it will go back to either MC28 or MC21 carbs as the PJ38's have no idling circuit...MC21 carbs are probably the best to go with if you have them.
I have also learnt that although a lot of guys on here are very knowledgable...they are also very biased and in my opinion they also dont always know everything they think they do
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My advice if its a streetbike though is top leave it as it is and enjoy it
. If you do modify it then keep us up to date with your progress and how it goes, and take any advice you can get from Neal as he seems to be having good results.