boring my 318

One way of doing it (Figuring it out) is measure how far down in the hole your piston is.
Thats the amount of room you have left. Then do some math.

3.58 - 3.31 = .27 / 2 = .135

If your piston is @ .135 down in the hole or greater, then the piston could technicly (sp) be used.