I'd experiment with the VIM1 and P281 images in my share with extlinux.conf edited to use the p271 dtb.
If you mod the 'box' image with the Amlogic u-boot bumerc shared you need to edit uEnv.ini instead of extlinux.conf - You will probably need to trigger recovery boot mode too. The recovery button appears to be down the bottom of the 3.5mm audio jack, hence it's often referred to as the 'toothpick' method. You need to hold the recovery button in as the board is powered on and then release it after 2-3 seconds (once u-boot loads) and this makes u-boot search for recovery files on SD/USB media; and it should find the autoscript files that load the LE kernel.