Originally Posted by G30CamperLance

I know that the 400ci is right in between big and small block so I am not sure if it will be the same for a 454 but its worth a shot



The chevy 400ci is a small block casting, but with Siamesed cylinders. Dimensionally, the block is the same as a 350...and the heads are the same (except they have some vent holes or something for cylinder cooling), Therefore the headers for a 265, 283, 302, 305, 307, 327, 350, and 400 are the same. Chevy did have a 402 Big Block that was a 0.030" over 396 casting, I think it was only produced in 1970...but for sure no later than 1972, and never came in a van.