Street car? I believe the OP’s intended use is street car, but nothing about this says street car except the rear gear. Oh that car will weight 3400+lbs. None of us are as light as we think we are! :)
I would be surprised if it weighs 3400+
I also have a 69 Dart. All steel, no glass anywhere. 8 point mild steel cage, frame connectors, 15 gallon aluminum cell close to topped off, carpet , stock dash , Yada, Yada. Only thing missing is back seat.
With 320 pound driver( me) in the car it weighs between 3310-3350 depending on exactly how much gas is aboard.
Had it on lots of scales. So to weigh 75-100 pounds more than mine when I am 320 pounds and carry lots of gas plus the cage .....?
Iron heads will certainly add weight( mine are aluminum ) but I am still 320 as driver and have the mild steel 8 point.