Not all trucks came from the factory with that bracket, mainly early 70's which later went to a "rod" style brace. Some came with rods for bracing. The angle iron bracket is said to not be the best way to support the tcase becuase it offers no flex, some say the rod isnt the best way. Only reason I want it is becuase I'm not lookin for flex, I'm buildin my truck for beef, towing and possible plowing.
Some adapter are said to be weaker than others, with that said a lil extra support helps out alot. 134lbs of iron hanging off a tranny adapter causes alot of stress. The big bracket bolts from the passenger side of the tcase using the 2 holes then gets bolted to the piec eof angle iron, whichis bolted to the frame..in between are 4 bushings.