""The guy I bought the car from said the engine came out of a 1970 Firebird...""
It could have , it was just that someone else swapped it some time before...lol
w/ "used cars" like these , lots of people think thats whats on the car is original, but very often they have been 'worked over' before...
Unless you can verify w previous owners....I would not take anything as 'the truth'...