They would both work, but, how much?!
I'm running a normal RRC flywheel on the back of my 4.6 with a standard clutch, no complaints so far. If off-road is your goal then I wouldn't choose a lightened fly-wheel either.
As for the dowel on the back of the crank, no it's not required and needs to be removed before fitting the flywheel. You also need some flywheel bolts as the auto-box ones are incorrect from my experience.