1972 Mustang Mach 1 Transmission Issue

I recently purchased a 72 Mach 1 Yesterday as a matter of fact
She has been sitting in a garage for the last 3 years.
After draining out the old gas and replacing the battery she started right up first attempt. Sounds amazing lots of care was taken with her.
But my problem is she will not engage in any gear. Shifts fine back and forth but I get no drive. Fluids are clean and advice would be great.

351 cleveland
BM Shifter Automatic

Thanks Ed