Moto Guzzi V700, V7 Special, Ambassador, 850 GT, 850 GT California, Eldorado, and 850 California Police models
The early headlight bucket (less common, typically fit to V700 models) was longer.
The later headlight bucket (more common, typically fit to Ambassador and Eldorado models) was shorter. The bucket was made by CEV with a part number of 02774.
Carel Windt has recently made me aware of a third variety of headlight bucket that is larger in diameter than the two common varieties mentioned above. In Carel's own words and photos:
Now I've stumbled upon a topic that the site has not been able to help me with. Most V7's have 7 inch / 180 mm CEV headlights. Some shorter, some longer as I understand. However, here in the EU we also have V7's with somewhat larger headlights, measuring 71⁄2 inch or 190 mm (outside diameter). These can be recognized by their mounts, they're slightly recessed into the headlight bucket. Please see attached images. I have seen them with some regularity, I always thought that the Special / 850 GT models had these headlights standard. However, US models don't seem to have them, and over here they are also not on every V7 Special or GT.