[Help] No LAN on install, Thinkpad T450

Hi all.

Snagged a cheap T450 yesterday to make a Hackbook, and I'm running into a pretty frustrating issue. I used the kexts and config from here, and the installer boots just fine; but there's no internet connectivity. The LAN port doesn't work (with either E1000 or Mausi), and using a phone (iPhone or Android) as a USB hotspot doesn't work either.

Which means that when I try to install, I get "The recovery server couldn't be contacted".

Does anyone have any pointers? Thanks in advance :-)

Edit: Important note - I don't have a working Mac currently. I've been using gibMacOS to download and create the installers.