What kind of flywheel is on a 73 340 four speed car?

The 340 flywheel that year has 1 or 2 big holes drilled into it to match the external balance of the engine. Most aftermarket clutches are fairly close on balance but not perfect. If I build an engine, I send in the clutch assy with the rest of the reciprocating parts so everything gets balanced together. For your application, I would go with something a little heavier duty than stock but not a race clutch. They can be miserable on the street.