Originally Posted by Vintage_Cyclist

If you put a shim on top of the pedal, consider that you might need to put a deep toe clip on that pedal. In this scenario, the shim would have to extend into the toe clip to level it's base with the pedal. MKS makes deep toe clips. Either that, or work repositioning the toe clip attachment into the shim, so it stays level with the new pedal base.

Another possible option would be to have your short leg shoe re-soled with a thicker sole.

I also couldn't help but do a little googling and found this: Cants and wedges

It looks like it can used to drop the pedal on the long leg crank, to compensate for the leg difference.Custom made for a 1/4" to 2" drop.