Big Block Fan Shroud replacement

To my knowledge, the 312 shroud is a one yr only piece. They are made for a smaller fan for one. I'm not sure about other differences. I know I barely fit a 17.75" diameter fan with mine. Thankfully, I've got solid motor mounts. I'd go ahead and use the 614 shroud for what you're doing. They bolt on to the same 22" radiator.