The fastest I have ever seen in person was a local guy that did a 48 Chebby for a customer at night and on weekends. He even pulled the body off the chassis to do the chassis and body work,installed a Camaro limited slip rear,327 chevy engine,and 4 speed trans. I THINK he updated the front suspension too,but can't remember at this point. I do remember stopping by his house on several occasions and seeing it as a work in progress,and how it advanced. I remember seeing the body hanging from two engine hoists,for example. I also remember helping him installing the engine and trans.
He had it all back together and running down the road in primer in 3 months. No kidding. All this in a 1 and 1 half car garage at home,and he didn't farm out any of it.