455's were not used in 1970 Firebirds at all.
Formulas were available with a 455 in 71-74, and they are very rare and very valuable. But not in 1970.
The 70 - 81 Firebirds had 4 models. The regular Firebird, Esprit (a luxury model), Formula (sporty), and Trans Am (sporty + expensive). Formulas had a much better suspension than the lower models, with a rear sway bar. The Trans Am was just a little bit better. A Formula with the firm ride option would be, mechanically, a Trans Am underneath.
The standard engine in a Formula was a 2-barrel 350 most years in the 70's. It went up from there to a 400 or (in some years) a 455. There were fender callouts for the engine size in a lot of years.
Here's a little tip about Pontiacs. A 455 looks just like a 326. Anytime you buy a Pontiac, the seller will always say it's a 455. You have to say how do you know? or you can ID the motor yourself.
