Okay, I removed some of the plastic covers on top of my motor, therefor I have "more" (= a little bit) access to the alternator.
I took a picture of the information on the alternator:
As you can see, it not only shows the part number from Toyota, but as well for Denso, along with another code (in the yellow part) which I don't know what it means.
I still find it weird, that even when you have the product codes, you cannot cross-reference (or let alone look it up) on the internet. Even Lexus and Toyota dealers I emailed cannot supply me with the necessary information (bolt type, dimensions and specifications). Sigh...
I also contacted Denso about their alternator, but they refer me back to my dealer, who doesn't know anything about the stock alternator. Very un-useful! :(