I had manifolds on a 451 in a 65 A and the thing was a beast, downright scary in turns. one little throttle blip and the *** was heading the wrong way. went to headers and it actually tamed the turns but I could not keep the smoke in the tires under anything but 2000 RPM and below. Went back to a warm small block. Much easier to manage and handle. Heck, I got a 6 in it now! 3 back is totally overkill. The exhaust has cooled and contracted enough within the mufflers that <2.5 is more than enough to get that out. 3 is a huge pipe and there aint alot of room for them back there over the rear and outboard of the tank.
