If the "button" is in a 93-94 that is an indication that the truck is one of the few that is missing ABS, full-float rear axle, and rear disc brakes. Unless the button was added after-the-fact.
The head gasket change came out after the end of 80 Series production. Additional metal was added around the end-cylinder fire-rings so that the head bolts captivated the fire-rings.