I recently finished an Outer Island and if I remember correctly I placed the front bulkhead 60" from the rear edge of the cockpit opening. I also don't use adjustable foot braces and my front bulkhead is padded out with 3 layers of construction foam board to fit my 6'4" frame. In my case I could have placed the front bulkhead a few inches further back. I do sit very nearly against the rear edge of the coaming.
I would suggest that you place the front bulkhead far enough forward to leave room for mounting adjustable braces if they were ever desired. For your own use those bulkhead sized pieces of foam weigh nearly nothing and provide a comfortable foot rest. Even if your bulkheads end up further forward than needed the foam effectively reduces the volume of the cockpit to its optimal size for you.
Also, until you have decided exactly where you want your feet to be you can just wedge the foam in place without gluing. That way you can add or subtract as needed.