Back in the summer there was a thread about a German product, a paste made of Citric acid and sawdust. I can't find it at the moment but I have been playing around with Citric acid for a couple months now and it has become my go to rust remover.
I have found all the other acid rust removers have some drawbacks to them but Citric has the fewest so far. It is very inexpensive especially the industrial grade, I didn't want to purchase 50lbs until I knew it was worth it so bought 10lbs of food grade. 2 cups of dried powder in about a gallon of water makes a strong solution. Your results may vary depending on the hardness of your water but it should be easy to repeat these results.
The test piece is from the KA24DE engine I'm using in the 510, 2 cups of Citric acid in a gallon of water, all I did was scrape the worst of the flaky rust off. The shop is cold, just above freezing, when the water is room temp in the summer rust removal happens a lot faster. If you splash some on your skin you just rinse it off, there is no drama, no burns.
These next 2 pics are after 20hrs soaking, took it out of the bucket and scrubbed it with an old wire brush and rinsed. The last 2 pics are after an additional 24hrs.
Now that might seem like a long time but I have lots of that so I'm good. Muriatic acid is 10x faster for sure but I have never found a way to completely neutralize it, the rust always comes back under the paint, so far that has hasn't happened with the Citric acid pieces.