I have a 1970 Mach 1 with a 351 Windsor. Just recently I've had an issue with the starter. The starter fails to kick out unless I put the car in gear. If I turn on the key to start the engine with the car in either neutral or park, the starter continues to be engaged after the engine starts until put it into a gear (drive or reverse). Has anyone seen this problem in the past?

 

take the starter out and bench test it and see if the drive is stickingand not returning when the power is off maybe simple fix or umight have a bad solenoid keeping juice going to starter when u let off on the key, also make sure the ign. switch moves freely. also mke sure the sloenoid has a good ground and clean connections.
ihave a 70 ranchero with a 302 and toploader 3spd. with some mild engine mods

 

Most of the time it's a cheap solenoid but since you say placing the car in gear corrects the problem. I'm going to guess the solenoid is getting power to engage the solenoid and staying there and placing the car in gear. Takes the neg off the starter solenoid when you take the saftey neutral switch out of park or neutral.