I took a risk and bought 5 gallons of Workshop Hero Metal Rescue Rust Remover. It was expensive, but the promotional videos looked promising. Water based, paint safe, rust remover? Count me in!
I filled the tank of the '83 KZ750 to the brim and a little less than an hour later the tank is clean and all the rust is just floating. This stuff is simply amazing.
I still need to flip the the tank upside down to get the top of the tank, but after that I plan on straining out the rust particles and saving this for the next bike build.