well as reference having a super light flywheel can cause alot of issues if not properly suited for the application. is a lighter flywheel always better than stock, YES. is a 7.5lbs drilled chromemoly the best, no...
my point is getting weight out is good to a point, getting off the line without a bog with super light stuff can start getting interesting...
to answer your question i think starting with a 440 source crank in 3.75, 4.15, 4.25, or a good used fueler 4.5" throw and then have it properly lightened, knife edged, driller, etc. along with a good .25 gram balance will go along way.