455 mounts in a Firebird the exact same way as all the other V8 blocks so no need for special motor mounts.

And yes, anticipate needing all the best cooling gear and tips. Huge radiator, OEM 7 blade clutch fan, fan shroud, fan installed properly 1/2 way into the fan shroud, 400 and A/C car radiator blocking plates, and minimal water pump back plate clearance. It's gets Phoenix like hot here in Central OK but with added humidity and my 455 warms up to the thermostat setting at 185 and that's it - no matter what the weather or driving speed. However I did put in a pricey Rodney Red aluminum radiator.

I have ceramic coated Doug's Headers for my 455. They fit with no issues and tuck up under the floor boards really well. Here again there are much cheaper solutions, but sometimes you get what you pay for!