Chassis Stiffening

What I discovered with my fb 68 barracuda is that the rear glass and support works seems to make the car quite heavy.It does, however help to get it to 47% rear weight bias It was hard to get my S down to 3256 # .I could lose a bit more if i tossed the GV, but that aint happening.
The Duster is likely 200 lbs or so lighter, with all same trim.Thats a lot of weight to have to get moving/stopped.