Hi,
Please note that IAP-205 doesnt support InstantOS 8.x. Maximum it supports is 6.5. May be 305 are shipped with 8.1 or greater.
The best way (if you dont have a console cable) is to connect these 305 in separate Vlan and let them form their own cluster. Once formed, simply SSH them by their IPs and check the version. If its on version 8.x, you need to downgrade them to 6.5