Since it’s difficult to do precision work with wood (i.e., since I’m too lazy to do precision work with wood), I just made everything adjustable. It seems to work just fine, for both the round and flat sanding attachments.
The belt tension is in the rear of the machine.
The flat sanding attachment required me to be a bit more clever, but it was still possible to allow the proper adjustments.
Here’s what it’s like to change the attachments.