Leave the head attached to the barrel with the 12 and 6 o'clock bolts. No need to replace the o-rings, they are still fresh.
Just slide the barrel out with engine at TDC keeping the rings in place. If you used sealant at the base, you have some cleaning to do and careful but awkward re-application. But no big deal.
Never underestimate the laxative properties of motorcycling.