Mike: Please post a pic of the date codes on each of the '71 4V open chamber heads.
I've researched the 71 4V closed and 71-72 4V open heads in the past didn't come across any 71 specific 4V open heads. To the best of my knowledge the D1ZE (both DA & GT version) heads were for the 71 and 72 model Q-code engines. Seems like there were only 500 or so of the 71 Q-codes made if I remember the Marti statistic correctly. The 71 Q-codes were made in May, June and July only. I know for a fact that M-codes were made as late as mid June 1971. I don't know the date when the first Q-code was produced.
Pat & Mike: The late 73 4V heads had smaller valves: 2.05" and 1.66", which coincidentally is the same as the 2V head.
Other info about this topic...
71 M-code: 300hp, closed chamber heads 2.19" & 1.77" valves, cast flat top pistons, 10.7:1 compression, Cam: 266, 270; .427, .427; 14-72-70-20; 34 overlap.
71 Q-code: 280hp, open heads, cast flat top pistons, appx 9.1:1 compression, Cam: 270, 290; .480, .488; 18-72-82-28; 46 overlap.
72 Q-code: 266hp, open heads, cast flat top pistons, appx 9.1:1 compression, slightly different cam from the 71Q and 4 degrees retarded, Cam: 270, 290; .480, .488; 14-76-78-32; 46 overlap.
73 Q-code: I don't have accurate info so I'm not going to speculate with what I think is correct...except for the valve size for late 73s is smaller.