Jake, I think you were in the right place but just in case you weren't, here's the drill down. Once at the site click on:
NTRAK and N Scale Model Railroading with Digital Command Control (8/10/04)
Installed Wired DCC Decoders in N Scale Locomotives (7/10/04)
Index to Detailed Instructions
Then you will see a list of locomotives and the Kato SD 40/45 will be on it. In this particular case they give you a choice of instructions to follow:
Aztec........the first one is a rather abbreviated Adobe PDF (you'll need Acrobat reader to read it) which I think talks about generic hard wired decoder installations
Aztec........the second one is another PDF, also abreviated, and talks about how to install a specific Digitrax decoder.
Col Andre Kritzinger - I couldn't get this link to work.
David Harris - this one looks promising and contains pictures and details on the frame modifications to install a Lenz LE0511W decoder. Couple of things. First, these instructions would also work with a Lenz LE0521W and you'd get BEMF. Second, at first glance this doesn't look like a real easy installation. I haven't tried it nor did I study all the pictures that closely but if you're timid about tearing the loco completely apart and then milling out some of the frame there are two other alternatives. First, go to Tony's Trains and I think you'll find they will install a decoder for you for a pretty reasonable fee. I've done this on several occasions and haven't been disappointed yet. The easiest thing to do is call Tony's (800 978-3472) and tell him what you're up to and he'll give you a price. You mail him the loco and a check and sit back and wait. The second alternative is to go the Aztec site and see if they have a decoder-ready frame for this loco. I haven't tried this approach but many have. My understanding is that you take your loco apart, mail them the frame and they mail you a replacement already milled. I'm told they also provide instructions for the decoder install.
So that's it. Thoroughly confused? There are pros and cons to all three alternatives and basically it depends on what your druthers are. Are you an adventurer, want to expand on your DCC skills by experimenting or do you want a locomotive up and running fairly quickly? And, of course, there's the cost involved............. Hope this helps. ...Tom