Hi to all in this NG

I rescued an HP 9000 / 300 with a label "Upgraded to 375".
I have no HIL keyboard.
I connected it to an external monitor an saw bootup messages, but it
requested kbd intervention.
I tried to connect through the RS-232 port, but couldn't obtain console
access, no activity. Of course, the settings were the usual ones
Now the questions:
1) There's a way to abilitate console access through the RS-232 port
without modifying PROM data ? As I stated, no kbd

The processor board,
only have a set of jumpers on the front.
2) There is an adapter HIL-PS/2 or HIL-DIN ?