Probably the easiest way is to sacrifice an Indian horncasting for the complete bottom end & do a straight cut & shut somewhere between the top & bottom.
If maintaining as much as possible of the original is the priority, then you could fashion an alloy piece to fit that could even be thicker to the outside, allowing for final linishing/dressing of the repair. The choice, then, would be how to secure such a piece permantly in place. If welding, a good welder might choose to stitch weld the piece in place to attempt to avoid distortions, with or without yet another piece of alloy as an overlapping patch beneath the piece & the main casting.
That probably would be the method which I would follow as it would be something that could be assembled to the correct geometry prior to weld. I would even affix all three parts with self tappers or pop rivets to get it into shape prior to weld (the patch would be stitch welded on the inside) with subsequent removal of the temporary fixings, which would then also have their resultant holes welded up.
However, hopefully other contributors to this Post will offer their opinions of viable alternatives.
Good Luck with it!
