I understand your query.
If you wants to use MAG SM-160's as only radius device and Since you are looknig MAG as just a replacement of your existing SBR server, Radius License should help your requirement.
When you apply your RADIUS appliance license, the applicable IC Series Device screens become available. You access most of the RADIUS configuration pages from the Network Access menu item available from the UAC category.
The below URL gives information on RADIUS Features Added with a RADIUS License
Also when you have only the RADIUS License, following URL has the information on UAC Features Not Available
I also recommend you to work with Juniper account/sales team for more information on this.
Note: If I have answered your questions, you could mark this post as accepted solution, that way it could help others as well. Kudo will be a bonus thanks!