Originally Posted by Wilfred Laurier

This rivet-or-screw plan sounds stupid - the area you indicate you intend to drill and put fasteners is probably the most highly stressed area of the part, and drilling will remove material and therefore strength.. Check ebay for a replacement left arm, or buy a new crankset.

There are a lot of equipment failures that you can happily walk away from. A broken crankarm is generally not one of them.