Back in the day, motor trend and car and driver reported specs and performance of most of the new cars. The problem with published quarter mile times is the many variables of weight, gear ratios, transmissions, tire types and sizes, weather and track conditions. Also, the factory tune changed moving forward through the years to meet emissions.
The Boss351 did have a better quarter mile than the 429 according to magazine tests, but consider the gear ratios, the amount of torque the 429 produced and trying to get traction on F-70 or F-60 tires, also track conditions and temperatures. Two or three tenths is not much considering all of the variables.
The Boss351 has an advantage. Its engine is lighter and shorter than the 429, meaning better weight distribution combined with less torque probably made for better off the line traction.
I think it would be interesting to test a SCJ 429 and aBoss351, both with stock engines, although allowing carb and ignition tuning along with slicks.
In the end, they are both awesome engines.