TODAY is a Great Day to visit our Store and order the parts you need for your truck ! ! !
http://forum.73-87chevytrucks.com/smforum/index.php/topic,12525.0.html should show you what you need.
It's the tension spring that fits along the length of the contact assembly for the key warning buzzer. Scroll down to image #30 in the following link posted by Zieg...