I am no expert on the subject but have spent a fair amount of time searching for spot lights and parts. I found a very nice NOS Unity spot light, which is most likely what your truck had on it at one time, at a swap meet for a good deal. At the time, I really didn't have a use for it but thought it was cool. Then I bought my GMC and it too already had a hole in the pillar so, use found! It took me quite a while to determine which Unity "bracket" I needed for my light that matched the pillar angle. Unity made a brackets for many different pillars, fenders and roofs. I searched EBay in vintage car and truck parts, https://photos.app.goo.gl/jcHURfGyUTxHGH3d7
for lights but try searching for Unity spot light brackets.
Check out the Unity site also to find your bracket number. http://www.unityusa.com/
Somewhere in there you can look up your particular vehicle and find the bracket number.https://photos.google.com/share/AF1...dnhrQ2l2SWJSXzZRYVZGZnkzWDkxbmJqX0lEZk5R