Allowable Bending Stress in Plate 1

I typically use 0.75*Fy for weak-axis bending in plates per AISC, even when the rest of the structure is in accordance with AASHTO. My experience has been that the particular component (base plate in this case) does not usually know to what code it's designed.

I agree. Hoping there was a code reference if a reviewer asks.

Thanks.