Welding and refinishing shouldn't cost much, but I'd be surprised if there wasn't a slight colour difference in the weld area.
Further thought - one way to mitigate that would be for the welder to use alloy from another scrap cover as filler material.
Doesn't work like that
It will be an Al-Si casting alloy, perhaps even an Al-Si-Cu
When these melt they burn off the silicon so they become more silver
Torch welding will work better than electric welding & when I do something like that either I bolt it to a sheet of steel plate or bolt it to the cases and stop the weld 1/8" from the end then let it cool overnight and finish it off removed from the cases.
These methods prevent the cover warping
As for using Allen head screws you should always spot face the bottom of the hole then use thick ( or 2 ) steel washers that are almost the same size as the hole.
Allens were specifically designed for clamping steel so the heads are too small for alloy .
