Left Hand side charging handle

I would to have it milled on the left side then have to bolt drilled and tapped with a handle screwed in to it. I have seen plenty of .308 with this done on the right side .
 
Can't speak to the left side but I've seen pics of British ARs with a right side threaded handle in bolt to make it a straight pull fast bolt gun due to their laws I guess. Only hitch I see in your idea is receiver stiffness being reduced. Maybe add a steel ARMS type rail to the top to help with that.