@Antony_Adshead It may not be relevant but have you tried @carlasella suggestion, in your linked thread, re your install problems on the newer iso:
It pertains to a different model, the N54L so may not be relevant but if it is it may work around your install problem, and potentially address the network issue also. Might be worth a try.
Strange that you are getting no network.
Let us know how this goes.
Can anyone else chip in on the install or the network issue with this hardware and Rockstor.
It may be that you could get more info, and possibly achieve a work around, by using nmcli to establish an internet connection and then use that to upgrade the system; which in turn may sort the network problem. Especially if you can subscribe to an update channel where you can pick up one of the newer kernels. Maybe you could temporarily use another network adaptor during this work around, if that is what is required. Also not sure of the system disk arrangement on these systems but it is entirely possible to move a Rockstor system, once installed, from one machine to another. I.e. install to a system disk on one machine, update it, and once all updates are in place shutdown and transfer the system disk to the NAS hardware.