You have the 3-4 lever upside down, or you have an OD gear box.
Had a friend in HS with a Mercury cougar and a three on the floor. 1st and reverse are on the same lever. He installed the lever upside down and didn't check it.
Fired it up to go to school the next day, put it in reverse stomped on it and drive right into his moms garage and smashed his crap up too.
