Hi David,My apologies for the delay but my team did provide more help! Below is the message they shared.Download the configuration file instead of downloading the image.
Please find the below steps to back up the stack configuration file:
After factory reset of the switch, firstly configure the stacking basic configurations like stacking ports, and unit ID numbering on all the switches individually. Connect the stacking ports and confirm if the stack is again formed like earlier. Now upload the previous backed up configuration file and with that, all the previous configurations (for example VLANs, port mappings, ACL ) should be retain.