That looks to me like it might be a CA spec '75 or '76 exhaust manifold with the full set of emissions integrations: one out the front and two out back, all blocked off at this point.
When I bought my '76 CA car it had similar/same (as I recall) manifold on it. I moved out of Ca and put a '74 manifold on it from a parts car. See photos:
- first is the '74 manifold with just one rear port, which I plugged (with plumbing cap )
- second is the '76 stock, with the heatshield on it so covering most of what you could see :/, but shows the front port
I'm in similar situation now, looking to make an upgrade on the exhaust overall which is tired and has leaks, and will start from the cylinder head mani/header back to the tail. Researching now for Spring work, and posted a few days ago on subject. So far based on my research (here on the forum and through friends knowlegeable) the resounding advice I'm getting is to
1. go with a header. Ireland Engineering is a solid recommendation, with a couple others in the mix; Stahl being another top one
2. from there back either build it yourself (from my friend who has welding equipment :), buy a nice stainless (like IE), or just get any decent system that will bolt in
This is based on my goals of:
A. fix a problem (leaking exhaust)
B. gain any HP possible with the upgrade
C. improve the sound pleasure: interior noise decrease (see A.) also looking for a little bit of burble out the back, but very streetable daily driver
D: be an upgrade that would be appropriate for a relatively near-term engine overhaul and slight performance mod
I primarily drive street, with fun in twisty roads, and occasional auto-x.