I've noticed some of these valve covers have a reinforcing ridge stamped on the outer mounting flange. Any idea when this was phased in? MOST '73's I've looked at have the plain 65-on up style. Some '73 and most '74's seem to have the reinforced type. On another note I see there is a repro of these, the passenger side one is missing the small rectangled mounting tab for the carb solenoid wire plastic support. Baffles me why people go to the trouble to make a repro, only to leave off one piece! 
'73 LS-4 454
'73 LS-4 454