I'm going to make some "in general" comments from my observations, over the years. I'll defer to FURYGT and others in your particular situation.
While the exhaust manifolds might bolt to the particular cylinder head, look similar to other manifolds, there can be some significant differences in the location, angle, and "clocking" of the exhaust manifold flange, where it mates with the individual head pipe or y-pipe assy.
In many cases, the angle of the flange can change as does the clocking/orientation of where the exhaust studs are located. This can make knowing the exact model year(s) the particular manifolds were used can be important, as you order OEM-spec pipes from normal exhaust system parts vendors or the repro vendors.
When I upgraded my '80 Newport 360 2bbl to factory duals, using salvage yard pipes, where possible, a one model year difference meant I also needed the matching exhaust manifold on one side to made with the "new" parts.
My '80 360 2bbl had a "new for '80" vacuum-operated heat riser valve. The '79 had the traditional thermostatic spring model, AND it was rotated 90 degrees from the '80 model, which also meant the exhaust flange orientation was different. So I had to go back and get the '79 exhaust manifold to install on my '80 engine. One more little thing not planned on, but needed. If I'd been going to a muffler shop to so the duals deal, they could have just built something, but as I was using OEM used parts, having to change the rh manifold was needed.
In looking at exhaust manifolds at swap meets, I've noticed the flange angle/clocking situation many times, for the same engine in different model years or body series.
Key thing is to KNOW what's on your vehicle and how it all hooks up. Sometimes, things which are perceived to be "all the same", aren't.
Just some thoughts,
CBODY67
