Yeah, those little details like form factor and mounting matter. :) I've been through a big ordeal just replacing the alternator on the BMW X5. They've used both Bosch and Valeo. They look virtually identical, but they require different pulleys. The different pulleys you could put on either one, it will fit right on, look at it, it looks fine. The difference is slight, so you could put it on and never notice. Until you go to put the belt on and see that the pulley is 1/4" off, out of plane with the other pulleys, if you have the wrong pulley. Even worse, some alternators come with pulleys some without. Some that are supposed to have the pulley, when you go to pick it up, it does not. Of course once you know this you know what to look for, but if you don't it can be a big surprise.