I wouldn't be worried about the rust being removed as I would be worried about it being dried and converted. Here's what's worked for me:
-I clean it thoroughly with a heavy degreaser, like purple
power or simple green letting it soak a little bit
-wash it off
-Dry the block with acetone and a rag
-Then I remove the loose pieces of rust with a wirewheel or whatever you have that you can get in the small areas, a screw driver ect
-Clean it with acetone and a rag again
-Convert the rust with Ospho. Sometimes it will take more than one round
-Paint it with a good rust paint like POR-15
-Top coat it with whatever you want
Watch your metallurgy and avoid hitting non ferrous metals with corrosive products like the ospho.
Cast Iron is very porous and takes some convincing to get the oil off of the surface sometimes. A good paint job is all in the prep
work and with you ending up with creaky worn out joints.