Call Protechfabrication, He can make you a very strong manifold. What kind of manifold are you looking for? Equal length? Tubular non equal? Here are some pics of there work. He has made one manifold for the RB20/25 so far but it's not finished yet. Mostly SR20 manifolds that go on fwd car and awd cars like the GTiR. He is very happy with the amount of room we have with the 240's. Wayyyyyyyyyyyy more room than a fwd B13-B14. some more pics http://www.3rdgearvtec.net/Andys%20Videos/Protech/ http://www.3rdgearvtec.net/Protech/ The RB one he is making is about this thick .
Here is there web page with the contact info. http://www.protech-fabrication.com/