> Thus, I can't "show | more", so I can't remember how to set the machine to
> autoboot.


Another trick is "show xx*" which shows the matching variables.   

Of course, that doesn't work unless you remember the prefix.  I often 
use it for "show bo*" to remember what the boot variables are called 
and/or see what they are set to. 
 
I suppose if you were really desperate you could do a search, something 
like:
  show a*
  show ab*
  show ac*
  ...

Conecting up a serial cable from a working system may be easier. :)