The 6303 board is booting and able to load a bootblock off a CF adapter and run it correctly. At that point I got annoyed with the free 6803/6303 tools available and decided to take a slight diversion.

I'm currently turning the core of cc65 into cc6303, as well as adding it to the Fuzix assembler (based off the freed up MWC one) and the linker I wrote. There may therefore be a delay before any more visible software progress happens on the board itself.