318 exhaust manifolds

Two basic choices. 68-71 340 "high performance" manifolds which would be the best option and are being reproduced, or 67-76 A-body 318 manifolds (72 and later 340/360 just used the 318 manifolds). You could also use 92-93 magnum manifolds, but there is no ready-made y-pipe for these since trucks had right side exhaust.