Here's nice used set of '67 GTO HO/RA repro D-port exhaust manifolds made for '64 -'67 A-body cars, complete with the required 3-bolt iron flanges and a set of 2-1/2" aluminized headpipes (or downpipes) that I fabricated. The '67 HO/RA manifolds are pretty universal, they also fit '68 -'72 A-body cars but are most correct for the earlier A-body cars. All of the
correct length Grade 8 bolts are included, something that these manifolds never seem to come with new (as far as bolt length is concerned).
The headpipes were fabricated using a short stub of 2-1/4" O.D. tubing that was expanded to 2-3/8" O.D. (biggest size that would fit inside the 3-bolt flanges supplied with the manifolds) and then flared to make the seal with the tapered face of the outlet. I took some straight lengths of 2-1/2" aluminized tubing to a muffler shop and had them put a 90 degree bend in each one. I then cut, fitted and TIG welded them to the stubs so as to maximize both flow and ground clearance as best I could.
One headpipe does have an abrasion on the bottom from a speedbump, but it only removed a little material and did not crush or dent the pipe on the bottom. Keep in mind that my Tempest is lowered a couple of inches and has a low-profile 17" tire (25.25" tall), you'll have plenty of ground clearance with these. I cut them off right next to the weld where they mated up with my Flowmaster A-body 2-1/2" dual exhaust kit.
The manifolds were run on my 455-powered '64 Tempest for about 5 years and 30K miles, there is absolutely nothing wrong with them. No cracks, stripped threads or warpage, the cast ductile iron material on these manifolds is far superior to the gray iron used to cast the original ones.
These ones have the larger 2.45" outlet inside diameter. I painted them with POR 15 gray exhaust manifold paint, still holding up pretty well and looks okay.
$375 shipped in the lower 48 states of the USA, a little more outside of the lower 48.