Will a 1968 Pontiac motor fit in 1978 grand prix?

It's unlikely a 1968 Pontiac engine will fit directly into a 1978 Pontiac Grand Prix without significant modifications. While both are Pontiacs, the chassis and engine bay dimensions changed considerably between those years. The 1978 Grand Prix would have likely had a much larger engine bay (to accommodate larger engines) but the mounting points and accessories (like the alternator, power steering pump, etc.) would almost certainly be different. You'd need to deal with:

* Engine mounts: The engine mounts are almost certainly in different locations.

* Transmission: The transmission bellhousing will likely not match.

* Exhaust: The exhaust system would need to be completely fabricated.

* Wiring harness: The wiring harness would need to be completely re-done or heavily modified.

* Radiator: The radiator and cooling system might need to be changed.

* Power steering and other accessories: The placement and type of accessories are likely incompatible.

While not impossible, the amount of custom fabrication and engineering required would make this a very challenging and expensive project, far beyond a simple swap. You'd be better off using a Pontiac engine from a closer model year to the 1978 Grand Prix.