Well, I have managed to get my Centris 650 up and running with NetBSD.
Thanks to everyone for their help and guidance.  Here is how I did it for
future reference in case someone else goes through his hellacious process.

A common suggestion was to up the RAM allotment for Installer.  Even
setting it to 25MB of RAM did not let me install the "base" file.  It bit
the dust at the same place every time.  I tried redownloading the base
file, but still no change.  

I went ahead and installed everything else that I wanted.  Fortunately, I
got enough of the base installed, that I was able to boot single user.  I
then used cpin to install the base file and used the instructions in the
FAQ for updating binaries to -current.  Namely, I did a  mount -a  and
then I did a tar --unlink and untarred it.  It boots fine now in both
single and multi-user mode!  Thanks to Ken Nakata for the hint that got me
there. 

I am sure that I will have more adventures, but now that I can boot and
pass fsck, I am think I am in good shape.

Thanks again to everyone for the help,

Mark