In reply to owen1988:
I'd hang on to it. Don't think it will have great value, tens of thousands of the were produced, and the (good) design remained very similar for decades
Keep an eye out for all the accessories, which if I remember will be a little metal meths bottle for priming, a priming windshield, small spanner, the jet-pricker, spare leather pump washers, brass screw caps for tank and pump ports, metal funnel, pan supports/ring and the instructions (possibly also a folding meatl windshield). Also for any spares kits that your grandad may have purchased
I have all of the above, but the tin had rusted in the garage. It still works (well it did twenty years ago when I last tried.......).
Its a lovely piece of manufacturing, and would be shame to sell for the little money you'd get.