Pontiac firebird engine confusion?

In 1987 a Firebird was available with a 2.5l four cylinder also a 2.8 and3.1 both are v6s. If the person you got it from said that it was a four cylinder then it would have a 2.5 and not the 2.8 and 3.1 because they are both v6s and the heads will not bolt onto a four cylinder