I'm looking to buy a new engine for my 79 Firebird, I was just wondering if a 67-69 Pontiac 400 would just bolt up. Currently the car has a Pontiac 350 from a 75 Firebird in it, with a TH350 tranny.

nope, you will have to change the motor mounts, unless the new block is drilled for both type mounts. the older ones have the rubber mounts on the motor the newer the rubber is on the frame

It will bolt right in. Its a given the mounts need to be changed.

Good luck!