Weight difference between glass and steel bumpers on 71 duster/scamp

I put a fiberglass bumper on the front of my 69 dart and just had it glassed to the stock inner brackets. This winter I'm pulling it and drilling it full of holes. When I did the rear last winter I made my own mounting brackets out of 1/8" x 2" strap. I bet bumper and brackets didn't weigh 8lbs.