Several sources confirm that the 239 Y-block has a 3.75" stroke. It seems like a 'gimme' to put this long stroke crank into a 292 to make a 331. Has anyone done this?

 

It's only 3.1". It was occasionally used to DEstroke Ys for class racing, back in the day...but there are some details necessary to do it.

The most common way to get a stroker Y is to start with a 312 crank & offset grind it, using the SBC rod dimension.

 

I bet your looking at the '39 - '53 flathead 239, 3.1875 bore x 3.75 stroke. Not a y block.
Andrew