With a bit of poking around the current git head of Fuzix now runs as expected on the 65C816 board. Although it all runs in 6502 mode I've taken a moment to detect a 65C816 and add optimizations in fork() to use MVN. There are a few other spots that would benefit similarly that I need to look into.
At the moment I am still running at 1.8Mhz. It should be possible to run a bit faster even with the current memory board.