I bought a 1968 Mustang with a 302, and 4-speed last week. I'm new to having a manual, and to a classic car. It's been starting fine until the other day. The starter spins and I hear a grinding noise. I took the battery and starter to get tested and they are working. Put a new solenoid on. I also tried to roll start but I don't have a long enough hill. Seems like the starter isn't fully engaging the flywheel. Should I try putting on a new starter? If that doesn't work, what should I...

Starter won't spin flywheel