I started by using the hand squeezer to dimple for the large #8 screws along the edges of the fuel tank skins. However, I decided to leave the nutplate holes along the inboard edge undimpled for now, since I wanted to be sure about which holes actually needed dimpling and that edge should remain easily accessible for future dimpling, if needed.
Then I got a box of 6d 2" (#13 6F1) finishing nails from Home Depot under the advice of the Slack group. These fit the Cleaveland Tools close-quarters dimpling dies perfectly and are much more durable than the copper ones that are included, and don't need any grinding to fit. With those, I was able to finish dimpling the hard-to-reach section of each of the fuel tank skins.
Finally, I went back to the fuel tank ribs to start scuffing up their flanges and double-checking that they don't need any more fluting tweaks to ensure their hole alignments are good. I'll need to continue with this though.