Best tires for stock 14s on 68 fastback

On a stock rim, I would say 205/70/14s would be just about perfect. You MIGHT be able to get away with 215/70s. If you want to try 215s, try to find a tire shop that will mount a 215 for you and test it on the ground for proper clearance.
FWIW, I went with 205s. They look good and don't rub on the front fender lip when turning into my driveway and hitting the bump at the bottom.