Bead blast the ARP's & then do the red scotchbrite treatment. The bead blasting helps 'dull' the areas you can't get to w/the scotchbrite. Then use the scotchbrite to 'even' out the overall finish.

Also, to hold the bolt by hand if using a bench grinder, weld a correct size nut to the end of a piece of round tubing and screw the bolt that you're buffing into the nut. That saves a lot of skin from being removed by the spinning wheel. You can also clamp the tubing in a vice for holding.