The ORIGINAL design for the tilt up wall would have included the necessary reinforcement (aka lintel beam) in the design of the wall unit. If the OP wants to WIDEN the opening this would void the original design. Therefore, I stand by my original comment, the OP needs to get the original house plans and possibly a structural engineer to review the original design to see if this is feasible.
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Pennsylvania, for 60+ years, most recently, Allentown, now TV. 
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