I cut up a piece of cast iron to fit the missing lug on this pipe:
http://i52.tinypic.com/35aryqe.jpg
That's a one inch hole in the other lug.

The pipe to start with:
http://i54.tinypic.com/dhekj7.jpg

Some expert welder will weld the lug on. I suppose he will have to
grind bits off the new piece in order to weld right to the middle.
I'll drill a new hole after the welding is finished.
I've not seen cast iron welded before. Anything to worry about?