I would like to cut out a large part of an interior laod-bearing wall that currently separates the kitchen from the dining/living areas. The section of wall I would like to renovate is about seven feet long, and I would expect to frame it with a stud and double jack studs at each side of this opening. Te kitchen currently has a 1-ft soffit above the existing cabinets, and the header would be on the outside of that soffit, so I can accommodate 2x12 dimension lumber. What size/material header do I need?