AFAIK, no airbags in anything domestic in '86, especially not an F150. Passive restraints were required to be phased in starting in maybe '86.
As far as retrofitting one, forget it. To install an airbag system that would be SAFE and reliable would exceed the value of the vehicle by a factor of at least 3 times. (since you would have to crash it to test your installation, you would have to buy another vehicle and duplicate your installation. If you got it right the first time, you would be good. If not, your cost goes to 4 times, then 5 etc)
If you want an airbag, buy a newer vehicle with a factory install that is in working condition.