Traeg - the $700 job includes a whole bunch of add-on bells and whistles, even a new ignition switch .... I would suggest that yes, you need a harness specifically for your TF truck, as it will have the correct lengths and layout and the correct connectors for gauges and such rather than a bunch of wires that need to be cut to fit and terminals added on .... OTOH, any of the vendors will have a good quality original style harness for the 55-59 at around $200
Bill