As I recall, the 7120 head saw the INTAKE ports changed, but not the EXHAUST. Therefore, your RENIX exhaust manfiold should work fine.
The confusion originates, largely, because the intake ports were raised for the HO head - and the RENIX manifold is not a direct fit. You can either notch the locating dowel holes to allow the manifold to cover the ports squarely, or just use a later manifold (one that came with the head, for instance.)
Given that the RENIX injectors are higher in the port, I'd be more inclined to use a later manifold - look at pictures of the early and late ports and you'll see what I mean. The RENIX ports have an "ear" on the top, to one side, which allows the injector to be mounted higher - which helps keep the intake valve cool by allowing it to be directly sprayed by the fuel stream (there are probably other benefits, but that's the only one that comes directly to mind...) There may be an interference issue with the earlier manifold on the later head - and I haven't had a chance to check into it yet.
So, the early exhaust manifold should work on the later head without modification, and the early intake will require some modification to the mounting system. The HO manifold would be best - but I do not know if the fuel rail will work with the RENIX system, since it uses a "pass-through" regulator with the regulator on the fuel rail and a return line from the engine bay (later models had the regulator in the fuel tank - but I don't recall if they made that switch for OBD-I, or for OBD-II...)
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