340 for Cruising and Fun 1/4 mile Passes

Check summit racing and jets for piston selections.
You can always call a piston manufacturer. A .040 340 piston should not be hard to find. Often they are listed in increments of .030. Which the next listing is at .060. In the past it was a normal sight to find a piston for any engine listed in .010 up to .060. Unless it was a known thing that engine could go further.