I finally got around to fiddling with this more. Eventually what worked was following the steps in After i2cset test, nano can't boot in eMMC boot evironment - #24 by shinichiro.adachi but using R32.4.3 linux and rootfs. Once it flashed and booted successfully I used I2Cset, no boot - #43 by shinichiro.adachi to correct the i2c issues.
Thanks so much for all your help, sorry for the slow replies.