Ian,
I have seen these on the 350 and 600EW brazed and welded on, more or less successfully depending on the skill of the welder. If more than two are broken, then you are better off replacing the whole top of the cylinder with a steel ring incorporating the lugs. This is usually only worth while on rare cylinders like the K/M32 series.
If welding up the lug, it is often better and usually necessary to braze/weld it up solid then re- drill and tap. Also the adjacent cylinder wall is likely to warp, almost certainly if welded, such that running a hone or a re-bore will be required.
Some pics of the K32 repair of how to go about it if feeling really energetic:
Badly repaired lugs.
Machining the new top flange/cross.
Orienting the flange for pinning, preparatory to silver-brazing.
Ready for brazing, one of the 1/8 inch blind pin holes can be seen between fins. Aslo the oppertunity was taken to fix some chipped fins around the head bolt. The K32 has bolts that go up blind into the head, whereas the 600 and later 350 EWs have the bolts through from the top.
Preheat for brazing.
Boring. This is just for show as the job was already done (there are no bolts holding the cylinder to the boring chuck!)
-Doug
[fix typos. -Doug 11Oct11][update image links to https. -Doug 12Jan20]