This is getting quite complicated. All I need is the 4 GPIO pins that are advertised!
I folowwed the instructions at
to modify the file
./imagebuilder/3.8/openwrt-imagebuilder-ramips-mt76x8_3.8/target/linux/ramips/dts/GL-MT300N-V2.dts
and added "uart1" to the relevant line.
I built the image again and installed it, but that didn't work. uart1 is still claiming pins 45 and 46.