The guy that I sent the cylinders to for over-boring found a crack in the center cylinder liner that I sent. In retrospect, you can see the crack at the 1:00 position at the bottom of the cylinder:
The guy had some connections and was able to purchase a used center cylinder that was in pretty good condition. After that he bored and honed the cylinders, then lightly chamfered the ports so that the piston rings wouldn't hang up on them. He also supplied the new larger pistons.
Before sending the original cylinders out for machining, I had them soda-blasted. They had been painted with black enamel. That was the look people liked in the early to mid-1980's, but this bike was a mid-1970's machine, and I wanted to get back to the bare aluminum finish. Also the paint was getting pretty flaky.
When the new center cylinder arrived, of course the finish didn't match the other two, so I had it soda-blasted as well.
Below: The engine with cleaned up cylinder studs, ready for re-assembly.
Below: The left cylinder, piston, wrist pin, retaining rings, bearing, and piston ring.
Below, all pistons installed. This time I triple verified the wrist pin retaining rings were seated properly!
Below: All three cylinders in place. I coated the base gaskets with Molybdenum-based anti-sieze, as they are notorious for sticking and making the cylinders impossible to remove without damage.
Below: Cylinder heads installed and torqued. Oil pump cover and brake lever installed.
Below: A couple of pictures of how it looked before I began. I definitely prefer the stainless steel hex-head screws over the rusty Philips head screws for the side covers.