I'm no expert either, but I just did a full rebuild of my F carbs a few months back and no way would I have been able to get everything cleaned up w/o removing them. Luckily, even though they hadn't been used in forever, the old gas didn't really cause much corrosion and the brass bits were still Keihin. Then they sat for a couple of months off the bike after being used with current blended fuel. I drained the bowls prior to sitting, and decided last night to have a look before reinstalling them. They were noticeably affected. Current fuel blends really are bad. I really think you need to remove them to get in there properly, and suggest you use soft wire like copper strands or nylon for opening the jets (if you aren't already.)
For gaskets, I bought the shaped version from 4-1, but two of them expanded when I dropped the bowls and I wasn't able to reuse them. Luckily I had the Honda non-shaped version on hand and got things back together. Your K bike looks like it has more room to work, but when I reinstalled, I found it worked well to install the intakes, then the carbs, then the boots from the air plenum to the carbs (although I admit those pieces were new and very soft.)