There's no reason to believe the p-o used anything other than the 4.3L clutch, is there? No reason you couldn't use it too, as long as the clutch diameter will fit your flywheel. If the 305 clutch is bigger- again, as long as it fits the flywheel- use it. But I doubt there's any difference.
Be sure to resurface the flywheel, and it's a good idea to replace the pilot bearing
while you're at it.