From where to where?

[Mastertech5]

If you've seen my most recent build thread post you know I got the body on today. After trimming a little on the bottom front on both sides to get a better fit around the lower frame where the welds are for the front rails that slant in toward the radiator. I clamped the body to the firewall and went to measure for the 45 1/2" gap of the cockpit . Does anyone know if your measuring from the edge of the front dash curve rearmost part of the curve. I'm assuming the vertical surface in the rear but they don't specify and there's a curve there too. The sides at the door openings don't sit all the way down on the sills either. Am I doing something wrong?