The guy before you probably used a pipe wrench, but hopefully
you can come up with something better.
It looks like my Mk 6 could have used an open end wrench on the
flats below the top most piece, but guessing the Mk 5 is different?
Can you use a couple of roll pins for the pipe wrench to engage
instead of directly on the flywheel nut?
Prepare to be boarded!