Have 88 firebird 305 tbi.bad .bought a older 79
olds 305 .carb .what do I need to do to make this
Not the place to discuss this - it is an intricate undertaking. Besides the obvious difficulties with fit and mounting, there will be issues with the older electronics, fuel delivery and wiring compatibility. I suggest you work with people on a Pontiac forum like thirdgen.org. They are focused on issues about these cars like yours.