No amount of rebuild kit will replace lost metal in those circuits.... The hole for the jet seems 'grainy' or 'crumbly' as in deterorating.
Toss the carb body and search for another one. Might want to search fpr another rack altogether.
In general, if one has a oxidation problem to the extent of losing metal then there's a strong possibility that others will follow suit once alcohol is introduced and then continually run through the carburetors, such as E-10 has been known to do.
Been my experience.
Single carburetor conversions are a perfect alternative (assuming the conversion is a quality one).
Personally, I don't like seeing the avenue approached out of desperation though.
A thoughtful approach to this choice needs to be taken, ..in my opinion. Would be wise to ask and learn as much as you can on this subject. Not all conversions are the same.