Issues and scope changes are part of demand management. So i suggest 2 options. 1. Create a custom field that store the security group name based on the project type and the custom field to be used in user access tab in request type. - This will be easier to maintain as there is only one Issue and Scope CHange type. The fields and process remains same but the people seeing them will be different
2. Create 2 seperate scope and issues request types and assign them correct security groups and also in project type settings. - There is a little overhead of managing 2 request types but gives flexibility to have different fields and process between them. completely independent.