One thing no one mentioned was the original factory finish. All the 60s and 70s Japanese bikes used a very durable gray paint on the engine side covers. Though often it's pretty much gone, it's a good idea to start out by degreasing, then use a paint-on paint remover, let it sit for 15-20 minutes then lightly work it over with a plastic bristle brush or Scotchbrite pad, then powerwash. Sometimes you'll be surprised by the chunks of gray paint that come off. But certainly if you skip this step and then find a weird gray patch that won't polish out, chances are good that it's paint.
Wet sanding also gets the worst of the oxidized material off the metal. Some castings like the strange valve covers used on the DOHCs, there are a lot of marks that will not polish out. The only way to get a good finish is to wet sand. Start with fairly course stuff, like 150, unless the finish is pretty nice already. Step down to 240 then 360 at least before attempting polishing.
Also, you do not need a commercially built bench buffer, as you can see from the video Magpie posted, a cotton wheel in any sort of arbor or bench grinder will work. You can also buy inexpensive adapters as pictured, that will fit threaded or keyed shafts. I scrounged a 2.5HP motor from a blown up portable compressor. With a 1" wide 8" diameter sewn cotton wheel on one of those adapters, I get great results.
For hand held tools, small angle grinders and die grinders are very useful but do be careful so the tool doesn't kick if the wheel grabs. But a great money saver for Dremel type tools - don't use the original little shaft and buffer pads (WAY too expensive). Use a long machine screw, cut the head off and grind the shank to fit your chuck. Use a few nuts and washers to clamp the pads on. You can do similar with a drywall screw (remember to round down the point) but the downside of the drywall screw is that the felts can grab the work and tear out their center, then they just spin on the screw.
