The V8 Valiant models are not covered in that printing of the FSM; if they were, you'd see listings for VV-2 models ("1" = 6-cylinder; "2" = 8-cylinder).
A data point: the 1964 Valiant and Barracuda ordering code list dated 16 April 1964 refers to cars with 8-cylinder engines, so the 273 (2bbl) was available at least as far back as that date, possibly earlier.
