You write: 
> Is there a kernel flag to tweak or disable the Spectrum console?

  I don't think there's any specific flag.

> If I boot with my spectrum installed, the console comes up on a
> screenmode that my plain-jane VGA monitor doesn't like. In the interim,

  I think I had the same problem with a Picasso board and a Zenith
Flat-screen monitor.  The default console configuration on the Picasso
wouldn't quit sync on the Zenith.

  I was able to tweak the console configuration slightly to get it to
work, but I don't remember what I changed at the time.  It would probably
be one of the parameters in the clconsole_mode data in arch/amiga/dev/grf_cl.c.

Michael
---
Michael L. Hitch                        mhitch@montana.edu
Computer Consultant,  Information Technology Center
Montana State University, Bozeman, MT     USA