It is!
Conceived and built in late 1960, the MK 5 was Bill Sadler's first rear mid-engined racer. Comstock Racing founder Chuck Rathgeb spied the car in Sadler's shop, and commissioned him to build a second example, and put up the money to sponsor both in the 1961 season. Seeing the compromises to his quality of life - his wife had left him during his 8-year building and racing stint, and citing differences with Rathgeb, Sadler closed up shop, and went back to work at Westinghouse as an electrical engineer. Moving to the US, he eared a master's degree in electrical engineering from MIT in 1966. Only many years later did Sadler return to cars, building a Formula V for himself, and participating in the vintage racing community.
Here's a shot of Sadler MkV reproduction (left) with a Lotus 19.