Well, I finally decided to get after fixing my cam chain. I put together a big summary about the F-Twins Cam Chain here (which I plan to update with more info after I successfully change mine). I have some recorded video of the change in noise that I experience when the bike is fully warm vs. when the bike has just been turned on (but after the cam chain tensioner kicks in). I'll post that soon.

I measured approximately 3.8mm of slack at the chains loosest point. However, I could also stick my ~8mm finger in between the chain and the top guide at that point.

Both of my timing marks line up just about perfectly, so I'm not sure if you can adequately use those to double check your chain slack.

Curiously, when I flipped over my valve cover, I noticed that I had two marks where the cam chain has started to rub. They are not that deep, but caught me by surprise.