Go to the local Auto parts store, buy a set of frame side engine mounts for a 1979 Camaro.
Go to the scrap yard and draw or take a picture of where the mounts bolt in on a Camaro.
Go home, bolt the new mounts in the correct location on your Firebird, then take the 454 with trans and all out of the truck and bolt it into your Firebird.
A little time consuming but not a difficult job. The hard part comes later.