Designed for B and E bodies.They may fit with minor work or not.The hedman shorty headers work well and are a breeze to install but you need a small starter.
put the headman shorty’s in my 68Ny with a 440, they are a drop with a 440 (not sure about a 400, but a 383 is not a drop in), ministarter and relocating transmission cooling lines is mandatory. Yes, they are worth the effort compared to a manifold in my opinion, and buy the coated ones. Don’t try modifying a b/E Body longtube for a c-body, the needed Work is pain in the a**, the torsion bars are at a different location in c-bodys.
