Here is a shot of the first successful campaigned rear engine dragster. It wasn't Don Garlits. This is a (poor) photo of the Kaiser Bros. digger shot in 1970 at Century 21 here in Colorado. It was a Mark Williams chassis and toured the country. This car went out to California in 1970 and got everybody's attention, including Big Daddy. Garlits spent about an hour going over the car. Big Daddy then went home, improved the design and built his own digger. 

I interviewed Mark Williams for a video I'm trying to do and he told me that he built that rear engine digger based on a front-motored car. That is, the relationship of the driver to the front wheels was the same. The idea being that a driver, used to a front engine car, should feel comfortable driving this car because his perspective is the same as a front motor digger. I don't know who built the body for that car. I believe that the body had some bearing on the car behaving itself at speed. The rear of the body around the chute was flared having a small "wing" effect on the car. 

Of course, Garlits went back to Florida and improved on the design and the rest, as they say, "Is history."