Angel:
Wow,that was a very complete and informative article. Interesting to say the least. I had to grin though, as I saw words/terms in there I had not heard since I was a kid in Mexico City.
One note, Mexican food and Mexican cuts of meat are very regional. Typically, what I have found anyway, is that at meat markets like "La Michoacana" are geared to Northern Mexicans and "Tex-Mex's" even though the name is "La Michoacana", which is really a generic name commonly used in Mexico for meat and vegetable stores that have fresh stuff. Thus, you need to be geared to ask what they will know. I would be really surprised if you could go into a La Michoacana and ask for aguayón or solomillo and they knew what it was.
For instance that article does not mention "Chuleton", which is a lower cut bone in ribsteak, or part of the ribeye. It is a very popular and favorite cut in Mexico, one I get often and it is good I recommend it. That article also mentions "panza" or "panzita", which is what I grew up knowing as what the Northern Mexicans and Tex-Mex's call "Menudo".
It also does not address "Fajita" a cut of meat, which it most certainly is. "Arracheras" are not "Fajitas". Fajita is a cut of meat, not a style. If you want there is a big thread from earlier this year on AO that dealt with this. I digress. Anyway, I like arracheras a lot but my wife, a Tex-Mex in skin color only, thinks they are tough. So does my halfbreed daughter. So when I do fajitas I get true fajitas as I have found them to be more tender, but with less flavor than arracheras.
Agujas, and Agjas Nortenas are also different, as are costillas and flecha de costillas. I would highly recommend that you get some fajitas and have them do what I mentioned above, and get a couple of agujas nortenas as well as 4-6 costillas cargadas and cook them all the same way and marinate the same. It should come out very well. I will be eating/making the above combo this saturday at a get together as well.