Link Types in Change Process

We are trying to include a task to create an Estimate (probably just a WTDocument) for time/money of implementation in our change request process. What link type should we use to associate the Change Request Estimate (WTDocument) and the Change Request? I don't see any OOTB links that make sense after looking at the definitions of the link types in PTC's documentation. We are not going to associate it as a regular attachment because the estimate requries special access control permissions. Would it be a better idea to customize the Configurable Reference Link? Has anyone else had problems finding valid link types for their associated objects?

Thanks!