Corner weights are the only way to sort ride height. A datum is what you need, you can fiddle to your hearts content afterwards. Surely you guys can find someone locally with some decent corner scales? I'd hit up some local club race, hill climb clubs and ask around. At worst you could roll up to a v8 garage and offer to swap the apprentice a carton of beer for his time to weigh your car while you adjust corner weights with ride height.
Fred Puhn wrote an excellent basics manual on developing stock suspension. Extract here on the topic.
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