To be clear, it was a few years ago since I did this procedure. And I also don’t have that exact controller (I have a G800+KR500) but should be quite similar.
Starting with the pots on the controller, I made sure that the analog output was within 0-5V on the full rotational span, as this is the limit of the arduino, but it should be as large as possible and with some margin. I think mine was 0.5-4.5V or so. This is all done with the pots on the controller.
Then the K3NG needs to be calibrated to this, it is done with commands, fire up a rotctl that you can manually send the commands with. O and F, then O2 and F2 with the full swing of the rotator.
The tricky part here is choosing 0-360 or 0-450, the K3NG code can have 0-450 and be calibrated for this, but then running rotctld with the max_az=360 to limit it’s useable range here. There are probably other methods as well.
Using gpredict’s monitor mode, move the rotator manually and verify that the position match. You can get in trouble if the endstops hits before it arrives at the full span as this can lead to the K3NG commanding movement to try and reach a position beyond the endstops.