I couldn't find a screenshot of the mech parts installer/tuner screens for ACForA on the web, but take my word for it that it basically looks like this:
Not very accessible, one will grant. So here's my proposal: (click to embiggen)
This will probably look familiar because it's a lot like equipment screens in your typical Japanese RPG. Using right and left on the directional pad, we can switch between the different components of the mech -- that's the list at the top. Currently, we're selecting a shoulder joint. On the right, it indicates that we currently have the Anvil Corp. Heavy Shoulder A installed and we're considering replacing it with the Hammer Corp. War Shoulder Model 60. (We can scroll between the different shoulder joints in our inventory using up and down on the D-pad.) A description is printed to give a bit of flavor of what this part's advantages are. Below that, the user is informed about all the parameters on the mech that will change if you install this part; of course we can go into random insane detail here, and indeed are obligated to since this is Armored Core. And fundamentally, we're done.
As for the rest of the user interface, the A button will let us install the part. The X button is used for fine-tuning the part -- which is on its own buried submenu in the original game. It would pop open a full-screen display that lets you see every random detail about the part and tweak it to the extent possible. The Y button is an instant test-drive. Push it, and the selection interface vanishes, the camera whooshes over to behind the shoulder or however the typical game view goes, and you're controlling the mech in an environment with a good selection of ground clutter and simulated enemy targets; getting back to the selection interface is just as quick. This lets you instantly see how the mech feels after making changes. B will exit to the main menu. And finally, the thumbsticks operate the camera, allowing you to admire your mech from all angles.
The result of this is a much more attractive, accessible, and efficient interface. The game is not dumbed down in any way -- it's simply a lot easier to understand, and get done, what you're doing.