wikipedia:De Dion tube is a non-IRS rear suspension, but with very low unsprung weight. It can be adapted to all Datsuns. De Dion is an inexpensive alternative to IRS. For roadholding and sheer cornering, it has no advantage over a carefully setup live axle (standard Datsun type), but potentially will have better ride quality due to low unsprung weight -- it removes most of the weight from the springs.