xd fairmont ghias arent stupidly rare but are getting very sort after for parts for the esp owners, the 351 helps make it worth more money than a six so yer not sayign its rare doesnt mean its not worth money as a 351 xds are becoming more sort after mate. this id thread might be of interest
xd-xe-xf id codes - xFords.com
also might be worth checking
xFords.com
sounds like a cool car you have there mate might be worth wacking up a picture of it