This is mine bought brand new in 2003. Its for the 273-318 but Im gonna run it on my 360 with two 500 Edelbrocks. Offys are weird- they never made a dual plane. This intake is an open plenum with a divider wall running center- front to back. It does not really have runners. The plenum leads into the head ports via windows. I wish Edelbrock would make an air gap 2x4 like they do for chivy. Offenhauser claimed an RPM range of 3000 to 7000 on a 273 and about 2500-6500 on a 360. I actually called and spoke to someone there back in 2002.