Alright I know there is a GS Stage 1, but did a Stage 2&3 ever make it out of the factory? According to this info they did
"1970 Buick GSX 455 Stage 3 (yes Stage 3 did happen and the engine block design is phenominal) (priceless car)
"Even the 1970 GSX 455 Stage 2 beats the two in question. (Stage 2 was an open production model) At the time it was the fastest production vehicle ever made. Yes faster then the 429 Boss, 426 Hemi, and the 454 Chevelle.