Get a "Ford" style remote
mount starter solenoid and run both key switch hot wires to the signal wire on the solenoid.
Jump from the large pole on the solenoid, to the small pole on the starter with some 4awg cable. Run a #8 or #10 jumper wire to the Start terminal on the starter, from the heavy pole on the starter. That will either be a ring terminal or push connection.
If you have an electric fuel
shut off solenoid to shut down from the key switch that shuts the fuel off, then you'll need to get a three position switch to be able to shut them down at either station.
With the key in the run position, both stations will power the relay and keep the shutoff switch grounded. When you turn either switch to off, the relay shuts and breaks the ground.