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

My 1972 duster weights 3240 with a small block and 8.75 rear end and a full tank of fuel (16 gallons) all steel and glass.soon to be a 512 with victor heads. Question what would be the difference in weight from a 8.75 rear to a Dana. What would I need cage wise to run low 10’s height 9’s and what would the weight be for the cage and frame connectors. One more question could I just run 5 gallons in my stock fuel tank so I could save 11galx6pds= 66 pounds from having less fuel weight in my car. I know I’ll probably need to put a fuel cell in at some point but can I do this or would the fuel slosh around to much and cause fuel starvation problems. Thanks Guys

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