Easy way to tell: the genuine article have the Weber name/logo and "Made in Spain" cast right into the body, whereas clones only have branding on a decal, tag, or ink stamp at most.
Note also there's two different models of Weber typically installed on our trucks, approximate mirror images of each other, so don't get tripped up by that. The DG-series are a newer design, somewhat blockier and tidier-looking than their mirror-image predecessor, the DF-series, which are a bit more rounded and busy-looking and have a diamond/oval-shaped raised flange on top that the DG*s don't.
IMO the DF-series are probably the better option for our trucks, as they can readily be oriented with the float bowl in front, which helps avoid stalling when braking to a stop, slightly leans the mixture doing downhill, and slightly richens it going uphill.
If you didn't perform the Weber swap yourself, it's also possible the PO who did used some other, older Weber model entirely, or something else similar like a Holley 5200-series which was a licensed derivative of the DF-series used on many US domestic models of the era and readily available from junkyards.
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