In the third generation of ADR there is a general safety rule, possibly ADR42, however due to the age of the vehicle you are building it does not apply. You must comply with national code of practise which basically is good engineering practise and "it looks right" tests, which are both somewhat subjective to the assessor.
The bigger hassle is complying with the emission standard applicable to the engine meaning catalytic converter, charcoal canister, vapour control fuel tank, non vented fuel cap and closed loop oxygen sensor engine management.
Having said all that, this is the situation in Qld; I don't know what the rules are for the latte set down south