I ran flatheads more years back then I would like to admit and one of the things I recall was that the throwout bearing was almost a 'consumable'. Now, if I were to have sat and thought about it "back then", might have figured out a way to add more "throw" at the cross shaft - that is changed the ratio between pedal throw and the final movement of the push rod. I have read the entire post, but don't recall if you discussed how you are making this operate, but unless it's hydraulic, you will have to make your throw changes with that cross shaft. Also, if you are using a 3 finger clutch rather then a diaphragm style, you will need to make sure each of those 'fingers' is being contacted at the same time. There used to be an adjustment - a bolt in each finger - that could be set for height. If it's a diaphragm type, and Mercury's as well as pick ups used them, those many individual fingers had to be contacted evenly as well. That diaphragm clutch was not the favorite of racers - you couldn't disassemble and add springs or change the existing that were too weak (we used valve springs for that) nor did they have the centrifugal weights to add clamping force