Usually when someone says they have "chevy rods" in their Ford small block, they are talking about the rod journal diameter. 2.100" diameter rod journals (standard SB chevy size) can be had pretty easily when purchasing an aftermarket crank and rods. The biggest advantage is less bearing surface. The less bearing surface there is, the less frictional loss there is. Another advantage is more bearing choices.
As for the long rod/more torque issue. I have always been told that a long rod motor will make more torque. I have never tested this theory and I dont have the knowledge to dispute it, so I have to agree with it.
As for the 400 Chevy crank in the 302 block, I am very skeptical of that.
Andy