Marc - having owned a later ABI caravan ('83 Ace Globetrotter 14' with sandwich construction and plastic windows) I do know that earler ABIs were substantially heavier because of their chassis, body construction and glass windows.
It was also true of many caravans in those days that ex-works (kerb) weights were under-stated. Our Ace was plated at 650kg ex-works / 800kg gross but in reality the laden weight was typically 900kg - provided all the components (tyres, brakes, suspension & chasss) weren't overloaded it wasn't an offence to exceed the plated gross in those days. EN1645 changed all that.
Sorry, can't actually answer the question.
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