Think about it logically...
The Bugeye body was made at Cowley, next to the ring road on the east side of Oxford, and shipped the 9 or so miles to Abingdon.
By this stage of the life of the conglomerate that was BMC, the Austin engine family had completely suppressed almost all other engine lines (this was before Jaguar and Triumph had been absorbed). The Bugeye 948cc 'A' series engine was built at the Austin engine plant at Longbridge (a southwest suburb of Birmingham) and shipped the 75 or so miles to Abingdon, down the good old A41 I know so well (lived 1/2 mile from it, drove it every day of the week).
At the time of arrival of these two major sub-assemblies at Abingon, what was on the body, what was on the engine, and what was entirely separate?
At Cowley very few parts were fitted to the shell before final paint, so you'd expect to see virtually nothing except the sheet-metal in body colour. In the Bugeye days Abingdon did much of the fit-out of the body, in later years Cowley did 95% of it, and Abingdon gradually became unviable as a factory.
At Longbridge all engines went through a paint line. I and/or my parents owned innumerable BMC cars, mostly Austins, through that era, and all of them were the standard green on everything, generator and starter motor included. But green wasn't the only colour. MG engines were painted black - the 1275cc in ncbugeye is black, since it came from a 1974 Midget. I am told Big Healeys ('C'-series engines) were painted a different shade of green. Morris engines were red (IMMSMR) and there were others of which I have no personal experience. So you would expect the original factory-fitted rocker cover gasket to be painted in whatever colour the engine received, but of course that would only last as long as the first significant overhaul. I do remember removing painted rocker cover gaskets when servicing reasonably new cars at the repair shop I worked at when I was at university in the late 1960s.
As for whether the manifolds were painted, you have to guess where they were fitted - at engine assembly at Longbridge, or at final assembly at Abingdon.
In ncbugeye's case the heat shield is black, but that could have been done separately at Abingdon. In fact the colour of the heat shield paint is a very slightly different greenish black whereas the rocker cover is plain black, so that is a logical conclusion.
Was the inlet manifold fitted at the same time as the heat shield? In ncbugeye's case, the inlet manifold appears to have no paint on it, and you would not expect the heat to have burned it off there, any more than on the spark-plug side of the cylinder head which is still black.
Exhaust? Was it fitted at Longbridge? My guess would be no. I think they would have put sticky-tape on the manifold face of the head and passed it down the paint line like that. Even if it was fitted and painted, of course you would expect it to have burned off.
How about the carburettors? There is no trace of black paint anywhere on the carburettors or linkage on ncbugeye. They may very well have been shipped in bulk from SU and set up by the Abingdon MG folks, after all they were the EXPERTS at all that stuff in those days.
More food for thought…