a 220-240 grit with lots of lube flow is correct for a cast ring, a 280 grit will work if that's all you can get, but get the style of hone with the 3-4 expandable parallel stones not the dingle berry hone
BTW
dust rust that appears almost in seconds on a completely clean engines easily wiped off with a lint free rag soaked, dripping wet in a mix of 75% diesel and 25% marvel mystery oil, and a cup of this stuff (BELOW) per gallon, as the mix absorbs water but prevents rust from forming