Yes...but there's an easier way.
Leave input-device set to keyboard and output-device set to screen, and
simply unplug the keyboard. When it can't find the keyboard, it
switches over to ttya for input and output on its own.
The point I was pontificating and pondering as a possibility presumes, perhaps, prior
persons
preselecting port 1 or 2 for the console, and since the OBP was directing output there,
you wouldn't
get output on the screen, which was the initial problem in the post,