Is the top ring a chrome faced ring? If so 320 grit. If it's a moly (bright gray in color) faced ring 240 grit.
They are moving towards a much finer finish than older ringsets. When I don't know I always defer to the manufacturer and every ring manufacturer recommends preparing the bore surface for a new ringset.
Cleaning after the preparation is important. Wash in hot soapy water,dry with compressed air. Then using a lint free towel with WD-40 wipe from the bottom to the top changing the wiping surface until it comes out clean,i.e. no gray honing remnants.
There's no reason to try something that isn't recommended and risk the cylinder in a nice Astro.
you don't see luggage racks on a hearse..........act accordingly