Had my cam chain done but...

[His Dudeness]

The casing is aluminium so it'd have to be tig welded which would mean getting the tip of the tig torch and a filler rod into that hole which could be a problem if there isnt enough access due to the size of the hole or if there was other stuff getting in his way. That'd depend a lot on whether the welder was willing to have a go at it. Also you'd probably have to machine the hole back to round or if its still all still bolted together maybe try and file it back.