My buddy at the Toyota dealer uses small (2"-3" dia) green Scotchbrite pads on a air-die-grinder deal, and it leaves a nice surface finish on both aluminum and iron - and removes all head gasket residue. I would not use it on newer heads that use MLS gaskets and require a fairly exact surface finish. I have seen these disks sold at Checker and even Walmart.
Colo Springs, CO
'78 FJ40, '89 FJ62, '98 4Runner