Push button dash

If the motor is locked, the transmission is not your problem. The trans can't lock the motor. The park lever controls a cable which engages the park pawl on the trans output shaft. This would lock the driveshaft.

There is nothing inherently "junk" about the push button transmission selector. Mopar phased it out to save costs, and industry pressure to "standardize" controls in the 60's.

When did the engine last run? You may have to pull the head to free it.