> AFAIK you only need to connect RX, TX and ground.

SGI din-8 is compatible with old-style Macintosh din-8 *for these pins
only* -- you will not get flow control with a Mac cable. ideally you
want SGI part X5-25TO8 ($50, back in the day), *or* the 018-8104 part
which might have been a keyboard adaptor or something.

i have piles of this stuff that's basically up for grabs -- several
i2 chassis, disk sleds, cables, etc. pay shipping or make arrangements
for delivery/pick-up in the "silicon valley" and i'll donate some, though
i'm keeping the prototype chassis, they're rack-mountable :)