I think those old coupes are just "tight". About 1995, I built the car of my dreams, a '36 3-window with a 276" Merc, a '39 box and '39 hydraulic brakes. After I was finished, I found it had two problems. First, the engine had too much power for the rest of the drive train, and second, it was very cramped inside, I ended up selling it about 5 years later when a local guy made me the proverbial "offer I couldn't refuse". "TagMan"'s comment is very interesting, as I considered moving the seat back, but since the upholstery was already done, there was no room without redoing it. Hopefully, you haven't had it upholstered yet, so you can do it right.
At the time, I was 5' 11" 235, so I wasn't that large

, but the car was just too cramped for me. The odd thing is that I never regretted selling it. I had bought it to replace my '51 club coupe (which I still have).