A little while back I picked up an 85 GT 4 speed that had been stipped down to the chassis from a friend who works at a body shop. The roof had been cut off because it was going to be used to build a kit car, but then they figured out it wouldnt work right, so I got it for free. The only reason we decided to take it was because it also had the 2.8 V-6 motor in it, and we were goin to do a swap with the 4 cyl we have. We took the block into the machine shop and they called us back and told us that it had a 3.1 crank in it. They also found out that the bore on the block was 3.4. The problem is that they dont know how to tell if the block is a 2.8 bored out to the 3.4, a 3.1 bored out to 3.4, or if it is just a stock 3.4 block. They said they couldnt tell from the casting number. Does anyone know how you would be able to tell the difference between the blocks? Could a 2.8 even be bored out to a 3.4? Thanks, Chuck.

A 3.4 block will have the starter hole drilled on the back side of the motor. This is the way they came in the 93-95 Camaro's and I believe on the crate engines.

The 3.4L pushrod engines have a large "F" stamped on the side. (same crank as 3.1L just a larger bore)
Yes some 2.8L can be bored to a 3.4L but it's not recommended for high performance engines.
The 3.1L is a 2.8L with a different crankshaft and pistons.
It could be a bored 3.1L as well. Not sure how to tell the difference between a 2.8L and a 3.1L block.