Join Date: Jul 2016
Location: North Louisiana
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A 400 & 455 should use the same mounts, in a '69 body.
Back in the old days, I used some Hooker round ports, on a 455 with RAIV heads. Used the same mounts as what came on the car. It was a '69 RA3 GTO. Never had any header to frame clearance problems, with 400 or 455 engines, and either D-port or round port heads. Used both Hedman & Hooker headers.
There are probably some guys around who can cut out a section of the tube and reshape it, for clearance. My engine guy has made lots of header tube changes. But, I suppose the possible changes would depend on the particular header and exactly what change is needed.
Last edited by bigD; 02-17-2018 at 06:52 PM.