Best Grit for Sandbalsting Frame Rails

1st up on the 378 resto project is dealing with surface rust and getting her good on the before doing anything else. What grit sand should I use? Is 80 grit good enough? I used it as a deck hand to get rid of rust while working the Lake Boats. Due to budgetary restraints its all they'd let us have it it worked very well, if not slowly. But I didn't know if anyone else had a second opinion? Also how many bags shoukd I get?


Side tangent: Going back to my first big boy job where I was a deckhand Merchant Marine on the lakeboats. Basically doing the equivalent work of a US Navy Bo'sin's Mate. Fightin' rust!