Sorry, guys....I never closed this one out.
I did order a 1966-70 B body dual diaphragm booster from Dr Diff and swapped it in a couple weeks ago.
Holeeee crap, the car stops great now. I was finally able to skid the front tires on dry pavement. The pedal effort is slightly reduced but the brake grip is amazing. I have 275-40-18" Nitto NT 05 tires with a soft 200 treadwear rating. The tires are sticky.
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