Caps have been used for emphasis of one form or another for a very long time ... though I don't recall specific examples of older texts using it specifically for shouting.
I do remember John Irving using caps in "A Prayer for Owen Meany" (1989), not to indicate shouting so much as to highlight the distinctive voice of the title character (described early on as a "strangled, emphatic falsetto"). A wonderful book and the caps emphasis, I think, really worked well.
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