Does a 427 cubic inch motor fit inside a 1999 Pontiac Firebird?

You can make it work if your willing to put the time into it. LS7 or a 427 Big Block? An LS7 would be the best bet because it's lighter and it's a high displacement small block. It's usually not your tie rods that need to be updated but certain circumstances it may need to but mostly your brake system needs to be updated to bigger disc brakes and multi piston calipers like brembo, wilwood, or baer. The rear end will have to upgraded. You can get a WS6 hood or you could get a high rise hood. Depending if your carbureted then you might get by with just a low profile air filter. If you're worried about noise run an exhaust system and run exhaust cut outs for the track. The main thing with custom swaps is to be able to be flexible because when making something work that isn't made for it perseverance is key.