If there's a notch in the top of the piston, or an "F" cast into it, that's the front. Wrist pin offset is to make sure the piston skirt is pressed firmly against the cylinder wall before the spark plug fires. Otherwise, you'll get a piston slap as the fuel/air mixture burns. It's usually possible to look at the wrist pin area and see that the pin is a little off-center. I don't think I've ever seen a set of smallblock Chevy pistons, except for really exotic racing stuff, that didn't have at least some pin offset. What brand are they? Drop me an email if you have problems deciding which way to install them.
Jerry
