I know arrange elements but it gives you only possbile to pack faces on padding 0 very near, there is not any option for one face on another like on screen. I will check textools.
Without TexTools, I would grab all the elements and select specific verts for flat aligning. As they would share the same space, it's just a matter of getting them stacked correctly together, then adjust the final shape of the shell to fit the texture area. Boxes and 90-degree shapes are faster as you can select multiple…