[ic] Search engines reindexing when moving to Interchange from another shopping cart

[John1]

We have recently moved a site onto Interchange from another shopping cart
and wish to encourage the search engines to reindex the site.

Currently, any old pages return the "missing.html" page which is informative
enough to a human, but from looking at the Apache logs it still seems to
return a Status 200 OK.

So, I am thinking of changing the missing.html page to the following:

########
[tag op=header interpolate=1]
Status: 301 moved
Location: [area href="index.html"]
[/tag]
########

so that any missing page is redirected to the home page and returns a
"Status 301, moved (permanently)".

Is this a sensible approach, or should I be doing something different?

Also, we have registered both the .co.uk and .com variants of the domain
name.  The .com is the main site, but we would like to forward the .co.uk to
the .com.  What is the correct way to do this so that the search engines
recognise the .com as the main site and the .co.uk as just an alias.  I
guess the first step is to set up a CNAME DNS entry for the .co.uk to point
to the .com?  But the only problem then is that the .co.uk address is
displayed in the browser bar if the user arrives at the site by typing in
the .co.uk domain name.  I would like the address bar to always show the
.com, but I am also concerned to ensure that the .co.uk is not seen as
duplicate content (that may lead to penalisation by Google).

I realise my last question is a little off-topic (i.e. not specifically
Interchange related), but I can't seem to find a definitive answer anywhere
else so would be really grateful for some help here.  :-)