At one point in time since switching from debian to arch I had figured out the extra bits you need to get TrueRNG to work, and I didn’t write it down and subsequently forgot how to do it. After just refiguring it out I thought I’d post it here since I’ll probably forget again.
Haven’t messed with Arch much, but that sounds about right. Typically the rng-tools daemon (rngd) points to /dev/hwrng by default. So yeah get the udev rules in to make /dev/TrueRNG. Get the rng-tools package. Modify the conf file to point to /dev/TrueRNG.