I had a very lucky day yesterday. I found a 68 flareside, long bed for sale for a fair price. The 300 was taken apart and the transmission was out of it. Its a good parts truck with a flare side bed. I bought it only for the rear bumper and brackets and know i can recover my money by selling off parts. Anyway, below are pictures of the brackets which are correct for my 66. I put a tape measure on most pictures so someone later on can identify the correct brackets.

 

Looks just like the set in my last pictures.