Hi andrew.mcdonald,
Please edit your nvidia-l4t-apt-source.list to r34.1:
deb https://repo.download.nvidia.com/jetson/common r34.1 main
deb https://repo.download.nvidia.com/jetson/t234 r34.1 main
Run below command to upgrade and install sdk components:
sudo apt dist-upgrade
sudo reboot
sudo apt install nvidia-jetpack