Pontiac Firebird Formula Drive Train Upgrade

I have a 90 model with a 305 auto. I also have a 1976 454/TH400 that I would like to swap in to it. Can this be done without firewall modifications?, transmount changes? or any other problems that may come into play? Thanks  

OK, aside from the fuel injection vs carb stuff, you need all the engine driven accesories, custom exhaust, a custom bracket for the torque rod at the the trans, a shorter driveshaft with the big yoke for the th400 (you will also be losing overdrive, so the shifter selector will not be accurate) and the trans mount will likely have to be modified to move it rearward.
You will also need heavier front springs to hold up that huge lump of iron and forget about your handling with all that weight up front. As for the firewall, it won't likely pose problems unless you have A/C, and the power brake booster and master cylinder may be tight to the valve cover on the driver's side.
Seriously though, unless the 454 has been rebuilt with better cam, heads and intake, you are better off with the 90 305- it likely has more usable horsepower and better mileage and emmisions to boot. The mid-70's big-block were not known for really great power per cubic inch, they were built to be high torque, low rpm luggers and don't perform very well in light cars because they run out of breath around 4000rpm. If you want a real performance boost, buy a GM 350 TBI long-block crate motor (just the typical pickup truck and caprice motor), add a Crane Compu-cam or other cam designed for fuel injected engines ie Comp Cams or Edelbrock etc. and an Edelbrock TBI intake manifold, use GM 350 TBI injectors in the 305 throttle body and a new chip for the ecm (Hypertech etc) and sell that old 454 to somebody that has a tow truck. Your performance will be better, you will remain emissions legal (most testers won't know it's a 350 unless you tell) and your mileage and handling won't suffer like it will with the big-block.
Just my thoughts on the subject, it's still your car!!  
A little help... 'cause we don't all have to learn the hard way!

Thank you for that. It was just a fleeting thought. The 454/TH400 is sitting in my 82 GMC Stepside that used to have a 305. It's a dog, but the engine looks good sitting between the fender wells.

As far as Carb vs Computer Controlled fuel injection. Considering cost and performance, It's carb all the way. OEM SFI or TBI does not cut it and I could replace the plenum and Intake manifold with a carb setup and I'll have less emissions and better power, and less problems. I have tested this theory in AZ.