Major assemblies, such as, engines and transmissions, may be substituted if the parts are from the same series car. A car may be updated or backdated without effect to classification provided the specifications remain within the boundaries of the model range for the car.

The degree of updating and backdating will, in most cases, affect the degree of class progression. Selective substitution, as opposed to complete substitution, will result in significant handicap. For instance, if only one or two major components (such as, an engine and/or transmission) are substituted from outside the model range without completely updating/backdating the car, then the car will gain handicap points under Modifications Not Listed Above and this will cause a jump to the Modified category. However, if a car should be completely updated/backdated, it would be classed according to the new (substituted) model range. For an update/backdate change to be complete, ALL specifications must be within the boundaries of the new model range.