Welding cast alloy can create more problems than it solves, the heat and weld shrinkage maybe locking in stresses that lead to cracking farther down the line, or distortion.

If it's only locally damaged ie no through cracks, and in an unstressed area then JB weld will sort you out. Just make sue the metal surface is immaculate and totally oil free for a full bond.

I could fix that.

Like suggested, I'd weld a bush on which I'd then tap a thread in for a bolt.

However, you'd need the motor COMPLETELY drained of oil.

You could probably just lie the bike on it's side for access.