Use Molly tubing to attach the parts!
If you want a guess based on other cars, you may get as much as 200#. Remember that the new stuff has to be hung on the car with additional tubing and how you do that will decide the final weight. I don't think your doors are 80# each or anything like that so the difference will be a bit less than most folks expect.
However, you will not get an easier 2 tenths of a second than lightening up the front half or your car if you get that 200# I guessed.
An aluminum engine block for a BBC will free up another 120# from an Iron tall deck block if you have that in the cradle up front to reduce in weight as well.
Bruce