Are you referring to the "Activate Extended Classic Scenario" configuration step in the IMG? Please note that this is just one of the configuration steps/activities for extended classic. There is no similar setting for the stand-alone scenario but there are a number of configuration steps to configure the SRM system in a stand-alone scenario. A few of these are number ranges, document types and attributes in the organization structure. Also, it's based on the business scenario you're planning to implement -- self-service, plan-driven, strategic sourcing, etc; might require different configuration settings in SRM.
What you truly require is the business scenario configuration guide, which you can download from service.sap.com/srm (link requires OSS ID to the service marketplace). This guide should help you in configuring the SRM system for stand-alone, extended classic or classic for the appropriate business scenario.
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