I just reassembled my 1st series grille (same as yours). I needed to disassemble in order to repair and paint. I assembled with big pop rivets (washers on the backside) and this worked well. My local Ace hardware store has a fantastic supply of nuts/bolts/hardware, including the "speed nuts" used to fasten the grille to the fenders. Also bought a box of 1/4" by 1" lag screws for a few bucks. These work as well as the stock lag bolts but don't look exactly the same.
