I had my 76 280 2+2 4 speed manual sitting for a few weeks and went out to take her for a spin today and cannot shift into a gear with the engine started. They just grind instead of going directly in. If I turn the car off I can put it into a gear and get it into first, but cannot shift into second. Anyone have any idea what it could be? Clutch or transmission?

Sounds like the clutch isn't disengaging completely.

Your car has a hydraulically actuated clutch. Check the slave cylinder (down by the starter, on the side of the transmission) and the master cylinder, for leakage. You'll have to peel the rubber boot back on the slave cylinder to look for fluid. Check the reservoir on the master cylinder for fluid.

You should be able to feel the clutch spring through the peddal, the difference in travel from before (when it was working) should be obvious.