Electrolysis - lots of info on the 'net. I've used this on antiques with success. It's a very effective way to remove ALL the rust, including the bore (must be done separately, carefully), with no elbow grease or abrasives.
For parts and the exterior, fill up a tub with warm water & washing soda (not baking soda), although I've used dishwasher tablets, they work too.
Suspend the parts you want to clean with conductive wire, immersed in the solution in a non-conductive container. [edit] place a steel anode, isolated from the parts you want to clean, in the solution. Again, lots of good tutorials out there. Then hook it up to a battery charger on LOW Now...POLARITY is crucial here, so I'm not off the top of my head going to say what side the +/- goes to, but - goes (I believe) to the parts you are cleaning; + to the anode (CHECK THAT I don't have my notes in front of me, although I've done this a few times now). Look into this, it works very well - even for finding rifling in 125+ year old rifles. Note that a pitted bore can still be shootable, even still accurate. Plenty of examples running around, some in my safe. Best of all - NO ABRASION MARKS from sandpaper or wire wheels.
Wish I'd known this when I started rebuilding old engines - would have saved me untold hours.
Side note - do this in a well ventilated area and be aware the water fizzes and your container must be large enough to contain it, or you end up with a brown slurry all over the place.
Good luck