Hello Dickon!

You wrote:
> In the beginning I seem to remember the machine booting with a console vt
> type of vt220.  Later kernels seem to have a vt100 console.  Is there any
> reason for this, and is it possible to change it back to vt220 again?

The reason is probably that the vt220 emulation is not complete. AFAIK this is currently worked on.
I think whether a virtual console acts as vt100 or vt220 is not determined by the kernel but can be changed in /etc/ttys.

Markus