Tach sticking? Good chance the two nuts holding the torque motor to the P.C. Board are loose. I've had three apart and all had vibrated loose. Use loctite on the nuts. (1)

124 speedometers can be adapted to the scorp mount including face plate but must be recalibrated when the scorp needle is used. You do loose the trip odometer. (1)

The air/heater vacuum control is a Chrysler product with # 58024 stamped on it. Late 131 controls look like they will work but have the labels rotated 90 deg. Dis-assemble and rotate buttons. (1)

Loose forty ugly pounds. If you do not use the air conditioner, remove it and plug the hoses for later use if desired. Without the compressor and condenser, servicing and airflow are improved. A late 131 or aftermarket rotary compressor is the trick solution. (1)