You will need to change out the master cylinder and the rod. As far as the exact difference between the boosters, call Steve Gregori at Brakeboosters.com
I personally have switched them out with never a problem on GM A-bodies. NOT SURE on The GM Full Size.
Dan
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1969 Chevelle 300 Deluxe Post Sedan Frost Green
1970 Buick Skylark Post Sedan Gulfstream Blue
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