I'm not sure what you mean by architecture, if you mean what full time professional architectural photographers mean by shooting architecture, especially interior architecture shots, then a 120mm lens might be a lens that you wouldn't use as often as a 90mm or even wider. I do a lot of what could be called architectural shots in that there is a building, usually a barn, old house, or something similar included in what some people would think of as more of a landscape shot. From a moderate distance on 4x5 this is one of my most used lenses for this type of shot, and yes, it is near a 35mm film equivalent of a 35mm lens. I do not use a super angulon, which seems to be a little bit of overkill on 4x5 compared to my angulon. Newer angulons are single coated, have so much coverage, around 211mm image circle, that you would have a very hard time running out of coverage on 4x5, but are really tight on coverage and very wide on 5x7and useless for most purposes on 8x10. The 120 angulons are smaller, cheaper, lighter, and will produce a sharp image within limts, meaning no mural sized prints, and meaning that you will be stopping down to f32 on almost every shot, especially when using extensive movements. If you haven't actually seen a 120 super angulon or comparable lens, you may be a little surprised at how big and heavy they are. If you want ultimate quality and 5x7 coverage, they may be the only way to go. I have what I would call an architechtural infrared shot in the gallery section. If you can borrow a 120 angulon you will be able to tell relatively quickly if it meets your needs, if you buy one you probably won't have trouble selling it unless it is in bad shape. They are not as easy to find as the 90mm angulon, so you may have to look a little while.
Good luck with whatever you choose.