How much weight gain from adding a Dana and roll cage.

My '67 Fastback has a Strange S-60, 8 point mild steel roll bar, sub frame connectors, and mild steel front bars welded to the fire wall. (removed inner fenders) 440 with aluminum heads and intake, 727.
I also have a fiberglass hood and trunk lid. Weight with me in it, and 1/2 tank of fuel: 3650 (I weigh 235-240)
How come the car is so heavy?