I need to verify some technical details. For example, in Mugen, the lifebar is often defined in the stage's .def file under [Lifebar] sections. The size and position are set with coordinates relative to the screen. At 1280x720, adjusting these coordinates to fit the widescreen without distortion would be crucial. Also, the texture of the lifebar—since higher resolution might require larger textures to avoid pixelation.
: If your new interface feels too quiet, you can customize the music by editing your stage files in the stages folder, specifically the bgm line. Mugen Tutorial How to change life bars Mugen Lifebars 1280x720