> /etc/ttys hadn't been changed since the initial installation, but 
> when I read it I was surprised to see it contains these lines:
> 
> # DEC 3000 Z8530 ("scc") serial ports
> ttyB0   "/usr/libexec/getty std.9600"   unknown off secure
> ttyB1   "/usr/libexec/getty std.9600"   unknown off secure
> 
> It seems, since these are both turned off, I was wrong in my 
> assumption that the alternate console port on the 3000/400 is driven 
> by a Z8530?

No. As you discovered, the kernel detects what device to use as a
console and presents it as /dev/console . I guess there is a
console ... on secure 
line. That means that ttyB1 should not be used, because
there would be two gettys on the same physical port which would not
work. That's why there is a comment:

# In normal operation, getty on 'console' pseudo-device is disabled,
# and is enabled for the correct 'real' device (e.g. one of the serial
# ports).

Don't do this except for testing, because (at least on my DEC3000 -
600) I observed that the ttyB1 device stopped working in -current. I
am actually curious if it is true for your machine too. But be sure to
have a way to access the machine if you want to test it and the
console stops working (I think that you already have it). Just turn
console off and ttyB1 on and reboot or send a HUP signal to init.

Bye	Pavel