I'm posting this on the assumption that there might be someone with
the same model of Macs and desires.  And also, who perhaps like me
would take forever to realize they had the printer cable plugged into
the wrong port. This took a long time because I was slow to realize
some things. Nothing in here is directly relevant to anything except
bringing up Open Firmware without MacOS.

OK, I decided I would use my iMac with Zterm and a Keyspan USB Twin
Serial Adapter in order to get to open firmware on my PowerMac
6500/300. I want to make sure I will never need to hook up a
monitor. (That I have both the functioning original video and a second
video card is irrelevant).

I tried repeatedly to get a connection after resetting the PRAM. No
luck. I decided that I was using the wrong serial port. I took out the
modem (which I suspect was not necessary, but in truth I have no idea)
and I pried off the plastic thingy on the modem port. Then I tried
again. Voila. 

Thus I accomplish the ability to do exactly what I was doing before
except now I have a disconnected monitor on my couch. I would love to
be able to function without the keyboard attached as well, but I don't
think there is a way as access to open firmware depends on the ability
to hit the option-command-O-F keys. (i.e. a way I can start from
scratch without MacOS and get to Open firmware over a serial
connection.)


-- 
Josh Kuperman
josh@ssimr.com
http://www.ssimr.com