Dan, In my way of thinking air flow is more important than compression ratio, you need air in the cylinder to compress. But the relief is old school, you need to flow air over the top of the valve to utilize the entire diameter of the valve and max flow. The combustion chamber in the head is more inportant than anything, can you post a picture of the head?
If you want to make the most HP use a turbo, flatheads really like turbos for a few reasons, one is of course to increase air flow.
Have done a few ford flatheads with turbos that made real good HP for a relatively stock design, 500HP+
Just my thoughts.
Harry
