I purchased the 5000# quickjack last spring for my '84 spider. Here is what i found. The frame slides under the car between the tires when it is all the way down, but it is close. however, when you start to lift the jack, the end of the frame starts to smash into the arc of the tire. So, I had to take an extra couple of minutes to use my floor jack to take the rear tires off first. Then you can adjust the jack to lift the car. As far as the rubber blocks go, they just barely reach the jack points when all the way out to the edge of the lift frame. My rocker panels are in good shape so i can put them just to the inside of the jack points and lift the car.
Hope that helps.