273 manifolds

They really screw the flow up because the ports are larger than the manifolds and this makes turbulance and impedes the flow of the exhaust at a critical point. There is a way to use 340 manifolds . A few guys I know changed the coupling on the steering colume to the box with a Jorgensens? swivel and got the clearance they needed to use the 340 manifolds. The 68 348 A body manifolds are the ones to use . Otherwise get the sawsall out and put in headers