You can get a standard LeMans flywheel and have it lightened. That's what mine has..
You're lucky it didn't explode . The history on the aluminum flywheel is interesting . It was never intended to last. It was a straight racing clutch and flywheel designed to last about 20,000 miles( a tad over 32,000km).
I bought mine with a lightened steel flywheel which weighs as much as the aluminum ( don't ask me how they did it but they did). I know they had some issues with the clutch(was switched to a standard sport clutch) later in the fix but now was done right with the proper Scura clutch .