You didn't say which car or year.
The headlights in the 1998-2002 Firebird are smaller than 4x6 so a 4x6 replacement housing will not fit.
The headlights in the 1993-1997 Firebird are 4x6 so a 4x6 replacement housing will fit.
"universal projectors"? Are those the poor quality plastic housings with a hunk of glass stuck inside to fool people into thinking they are projectors?
Those typically have poor output. They are not real projectors.
You can clearly see the bulb and there there isn't a cut-off shield. Also the blacked out ones are worse.