It is not the load on the beam that would concern me but, rather, the loads on the joint. Joints are far more complex to analyze than a beam. The design loads are based on intimate contact between flanges and you cannot guarantee that your shims are going to give you anything approaching full contact. For such a critical joint I would make sure the assembly matches the design.
2017 Donation: Complete
RV-14A Empennage Kit #140396