The latest brackets are like 22 gauge sheet steel; very light. The "tractor seat" spare tire holder is part of an old aluminum frying pan (the originals were steel). I also made the brake reservoir bracket out of sheet aluminum, and also the central clam pins (those were steel on the originals too).
Nothing I added is all that heavy, with the possible exception of the chassis tube extensions up front which by necessity (i.e. to be able to support the weight of the front end of the car over a jack) are DOM steel and weigh maybe 6 pounds each.
The gas tank cover is probably another 10-12 pounds.
I guess all-in I've added 40-50 pounds of nonsense to the car in my quest to make it look more like what Wendler released in 1955. Running the plastic windshield and alloy wheels probably puts it back close to where the kit would have been if assembled as McBurnie intended.