You'd be better off buying a complete set of track plastics that include the bellypan, as they will fit the standard mounts (just remove the headlight) and won't trash your original plastics in the event of a little lay-down!
Something like this (and a couple of spray cans of paint!) would be ideal:
http://cgi.ebay.co.uk/ws/eBayISAPI.d...m=310112622950