Also looked like you might be able to shift the diagonal tube vents down just a smidge, and it would clear the text.IMO, you should go back to labeling the positions numerically, like the pic on the website.
Then, have the numbers and corresponding frequencies listed across the top, below the in/out/DC text.
It might "clutter it up" a touch, but it's better than the frequency being cut off by the vents.