It looks like the pawl for the ratchet that sets the brake is missing . I looked for a diagram on this forum . I found one on Fordifcation , but it isn't detailed enough .
My question is can I get this one part or should I start looking for the whole assembly? Also what years interchange ? The truck is a 75 F-250 4 wheel drive .

 

Had the same problem on one of my trucks, I changed out the whole assembly. I don,t think they changed over the years, but I could be mistaken.

 

The parking brake actuator was only sold as an assembly. The only parts that you could buy separately were the pad for the pedal and the release handle.
Early '73 models were a little different but the complete assembly interchanges between different year models.
The part number for the assembly is D3TZ-2780-A, unfortunately no Ford dealer or obsolete parts supplier has one.

 

1976/79 is different and there are two different types.

1976/79 F100/350 & 1978/79 Bronco:

D6TZ-2780-A .. Park Brake Control-Use without Luxury Décor / Obsolete

D6TZ-2780-C .. Park Brake Control-Use with Luxury Décor / Obsolete

No Ford dealer or obsolete parts vendor has either one.