It's simply called a backplate

probably the wrong number, but still: you could give a bit more info: The drum diameter is for one a good start to notice. Probably something like 180mm

Are the brakes ' self-adjusters' (with a wedge adjuster) or do they have the toothed-ring adjuster?

Since it's a 1303, many parts might actually fit from a Golf 1 / 2

Good luck!

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