i think the 4-2 part is the same as normal b16's mate, but the 2-1 part is the more desirable part as it has the 2.5" collector.
I would try advertiseing it on civicsportsclub.net or similar sites because ek4 owners love these for the larger collector. I think they usually go for around £80..?
Good luck with the sale.. oh and sandwiches is a top bloke to deal with
ye, thinking about it, civicsportsclub has been down for the last week or so. The site is a bit rubbish because its always crashing, but things sell quick on there (when its working).