I actually read somewhere that Zero pilots could switch some gauges by personal preference, and historical pictures seem to back this from what I've seen. Or perhaps depending on the manufacturer they were just different I'm not quite sure.
As far as production, I'm not really sure myself. Although I've seen rough estimates on total Zeroes produced during certain times, it isn't specific on the model. Here's what I've got anyways....
                               Mitsubishi     Nakajima     Total
Mar 1939-Mar 1942     722             115            837 
Apr 1942-Mar 1943     729             960            1,689 
Apr 1943-Mar 1944     1,164          2,268          3,432
Apr 1944-Mar 1945     1,145          2,342          3,487 
Apr 1945-Aug 1945     119            885             1,004
Total                        3,879         6,570           10,449 
Anyways, can't help but feel like were hijacking this thread so much to my displeasure I'll stop here.