Megy,
The difference is in the length of the downpipe and catpipe on the 2.5 (Hawkeye) against the 2 litre (blob and bugeye) the overall length of the combined parts is the same so, if you went for a full decat dowpipe you would get the same one piece part for both but, if you only wanted to replace the cat pipe it is model specific.
Centre section and backbox are interchangeable between the 2.5 and 2 litre models
Hope this helps?
Gus