Looking good.
The exhaust was actually via the supercharger outlet, in the 'blister' under the rear fuselage. This 'blister' was stainless steel, and often had some discolouration (of the steel) at the forward edge.
The outlets either side of the nose, behind the twin shutters, are the waste gate. There was sometimes some staining here, but nothing like you'd expect to see on a 'standard' exhaust outlet. That said, some photos show relatively heavy staining, whilst most show minimal, if any staining. It's a case of trying to find a clear photo of your subject, or failing that, one from the same unit, and replicating that.