All 64-67 Chevelle 2-doors had those pieces on the wheel houses. I'm not sure, but I think their purpose was to help catch any water that comes down from the quarter window and route it down to the drain in front of the wheel house (in the rocker), rather than allowing it all to run down into the pinch weld between the quarter and wheel house, or back into the trunk. Since you have it and it appears to be useable I would certainly put it back rather than leaving it off.
The other two pieces you show were on all 66-67 coupes, and basically they reinforce those two areas and help tie together all the various body pieces that meet there. Again, since you have them, I'd use them! No reason to build it back weaker than the General built her!