Jimbo. Look on the brightside. You can read the part number without bending down. As for the airway, its function is marginal anyway, and as bergs says flash there is common. My guess is that the blocks are sand castings and swapping the number blank was a good way to add a bit of variety to the job. Almost like a signature "Yeah, I done that one!" Give it a light probing, it may be rust or muck. If its solid, don't worry.
More important with a used barrel is good threads and undamaged cam follower tunnels. Hairline cracks on the lower skirts of the bores, by the cutouts, sometimes appear, but are easily repaired.
We like to think these bikes were made by enthusiastic and caring individuals...It ain't so, and on the line you can bet one or two or more were not perfect especially if the foundry chargehand had given the guys a good gobful for some minor cock up. I think management these days is of a more enlightened style.
Swarfy
