By 1970 the cost of insurance on the big block Supercars was very high. That may have contributed to the cancellation of the 1970 454 Yenko Camaro. May be why Don called the LT-1 70 Nova his insurance beater. The 1970 Camaro was released later in the year and that may have been another factor. There probably wasn't much of a market for a 1970 Yenko Chevelle with the release of the 70 LS6 Chevelle.
In 1971 the DOT and NHTSA was cracking down on exhaust emissions and safety standards but Yenko was working on a COPO 400cu.in. small block Camaro with a 350hp hyd cam and LT1 intake and Holley. A prototype of this car was tested in Car Craft Magazine. This 71 Yenko Camaro was also a no show.
I have been looking for information on the Yenko Stinger Vega. According to one article, Yenko sold the Vega as a non turbo in 1971 and sold the turbo kit over the parts counter. He was trying to build the 1972 Stinger Vega as a COPO car with special pistons for the turbo and other parts but may have had problems getting it past emission testing. Adding to the Vega confusion is the ad for Group 7 Filters sweepstakes with first prize listed as a 1973 Vega Yenko Turbo Stinger.
I don't know what to think of that document on the 1973 Yenko Camaro. It doesn't even look like a street legal car in the picture.
This is a clip from "Agent 1320 Reports" in Dec 69 Super Stock Magazine.
The "little guy in Pennsylvania" I guess would be Bill Jenkins?