It's good that you're going through the list Teddy. You can eliminate scored slides as a cause of fouling - from memory, your slides actually looked in good nick, but even when badly worn (like right through in heavy 'chafing' areas) it won't cause plug fouling.
Not sure why you can't get ignition timing spot on for both cylinders? You can make a very slight increase or decrease in points gap to allow the timing to be set within the available slots.
From what you're saying, you are getting uneven readings using a vacuum gauge to set the carb sync?? It really isn't necessary to use vac gauges on twins if you're just getting the thing running (and TBH I've never used vac gauges on my or anyone else's twins) - for initial startup just wind the throttle stop screws right out until the slides seat in the bottom of the carbs and adjust the cables so the slides both lift at the same time. Again, slide wear won't make any diff unless severe.
Really sounds to me like an ignition system cleanup will do the trick - all contacts (including if you're running everything through the main key switch ie no relay), contacts through switch blocks and onto coils etc. A weak spark would likely cause plug fouling.
