Last time I was looking for an alternative alternator I went to a couple of wreckers with the old one & just compared it. They had shelves of them ready for easy comparison, available for sale then & there, they were cheap & came with a gaurentee.
As far as Japanese built nissans go, there are multiple brands of alternator in multiple sizes used in multiple mounting locations on each model. Thankfully they share common mounting bracket dimensions in many cases. I found the electrical connection more variable. The pulley varies too (diameter, offset, number of grooves, vee vs multi vee) but is mostly interchangable between similar alternators.
You'll see the same alternator in left & right hand configurations, and what appears to be the same alternator with different current outputs. Some brands are more reliable than others...
As far as the K11 goes, it physically looks similar to alternators on cars with higher electrical requirements.
If you have a look at 90's nissans (e.g. U13 Bluebird / P10 P11 Primera / Maxima / Cefiro) for example, you'll typically find 85A to 95A examples, which are quite a bit bigger than K11.
