[tom420]

Okay. I've been up, down, and around, this 1978 Pontiac 400 4BBL Trans Am issue for three weeks now and I still have no idea what block is supposed to be in my dad's 1978 Trans Am bought new from the dealership.

My dad died a few years ago and left a 1978 Trans Am, which he bought brand new from the dealership to my brother. Just before my dad died, my brother managed to blow up the original engine. My sister, worrying that my dad would find out and do unspeakable things to my brother, took the car to a "backyard" mechanic to get it back on the road before my dad found out.

The "backyard" mechanic pulled the original motor and slapped in a worn out Pontiac 301 with an adapter to bolt up the TH 350 auto which my brother promptly blew two years later, thankfully after my dad died.

Now, I've been tasked to return the car to the original numbers matching beast it was.

Unfortunately, the original block/motor is long gone so I don't have original casting numbers etc.

I need help identifying what exact block was in the original car.

The build sheet lists the motor as "L78" which some sites say was the 500557 block. Other sites say it was a 568557 block. To throw massive confusion into the mix the car has the T/A 6.6 decals on the hood scoop which I have been told ONLY came on the W72 1978 T/As. Granted my dad could have added the decals after he re-painted the car in the late '80s but I don't remember. My sister is trying to find some original pics from the '70s when he bought it.It also has the "WS6" performance package.

I'll attach the original build sheet. I need to return the car to numbers matching so I would appreciate if an expert could guide me in the right "block" direction at least.