If you want an extreme rate of lift, why not use a roller lifter? The same multi-piece pushrod setup could be used, or just extend the lifter body up a few inches into the pushrod chamber. Iskenderian used to sell a flathead Ford V8 cam/lifter setup with a radius on the bottom and a groove in the side of the lifter. It had to be pinned into the bore to keep the radiused part of the lifter aligned with the cam lobe. It was a short life race option, but it allowed for an almost square cam lobe. I think Isky called it a "404"- - - - -indicating valve lift in thousandths.
Isky also made cam setups that used mushroom-shaped lifters that had a much larger foot than the body of the lifter. The block had to be spot-faced with a special flycutter to allow the lifters to be inserted from the bottom and rise high enough to install the cam. Those cams had extreme lift rates, as well.
Jerry
