Yeah Strip... I saw this thread and looked at all of those too.  Looks like for early war, the M16 is about the best there is.  I did find this though:
Cannone da 90/53 (Italy 1941 - 1943)
Caliber     90 mm (3.54 inch)
Barrel Length    4.736 m (15 ft, 6.5 in)
Travelling Weight    8950 kg (19,731 lbs)
Weight in Action    6240 kg (13,757 lbs)
Elevation    -2 to +85 degrees
Traverse    360 degrees
Muzzle velocity    830 m/sec (2,723 ft/sec)
Maximum Ceiling    12,000 m (39, 370 ft)
Shell weight    10.33 kg (22.77 lbs)
But... according to all the sources I found, MOST of these guns were made to be either fixed, or towed.  Only 57 are known to have actually been placed on trucks.  Yes... I had to Google my hiney off to find it.  Found it on Wikipedia first, ignored that, but 2 other sources backed it up.  Here was the best one:
http://www.comandosupremo.com/Cannone9053.htmlSo with only 57 on trucks, it wont fit into the criteria to be used here as a self propelled AA gun.  Not to mention, it has lees protection around it that the M16 does.