I always use my fwd bulkheads as my footbraces, so that measurement is made based on seat position and leg length! I leave the length a bit long so that I can make finer adjustments using foam

I always put in my bulkheads (4mm plywood) before I attach the deck to the hull. I make sure that there is a tight fit between deck and bulkhead. Then I add thickened epoxy on the top of the bulkhead to make sure there is a good seal to the deck. When I clamp the deck to hull, I make sure to put a strap around the bulkhead to make sure that the deck is pulled tight. Afterwards, I do a "light: test to see how tight the join is. Thickened epoxy or other sealer is used to fill any gaps.

Just my way,

Sean