Ive given the whole thing a good clean with wire wool. Turns out all three throttle levers are different. Two of them look like different generations of the same part, as they both have a D and 1498 on them, but the number is in a different sized font. The third one clamps differently and has no markings. Obviously the levers could have come from anything and may not even be relevant to this manifold at all
What confuses me is how the manifold is bolted to the engine. the bolts at the top would be fairly short, studs with big washers and nuts maybe (like the minor) but the lower mounting bolts would have to be much longer, well over an inch long sticking out from the engine. Unless there is a big step in the shape of the engine casting?
Also, it looks likely that there is something (presumably an exhaust manifold) sat right next to the ports, on the inside AND on the outside of this manifold, due to the straight edge and shorter fins, and not a complete hole for the bolts to go through, only an edge to rest on. This suggests the engine has at least 4 exhaust ports. Also most of the older car engines I have seen have the manifold mounting bolts on the same height as the ports themselves, whereas this has the mounting bolts above and below, and at an angle.
A mate of mine who works at a bike shop over in the isle of man has taken the photos in to see what some of the gurus there make of it. This should hopefully narrow it down as to whether it is from a bike or not. The asymmetric shape would mean that the float bowl of the carb doesnt stick out at one side hitting your leg/knee... which argues in favour of bike origins.
It had better be from something interesting after all this research!! see attached photo of the throttle lever. Why are there little brackets above and below the D??
Picky<br>

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1969 Four door Saloon Old English White 1275 with ported head and HS4 carb. Wolseley 1500 front brakes. Currently off the road with a leaky master cylinder!