I have a set that I just put on stock rods from KB? Without machining? Did you buy the right piston? Used KBs (silvolites) for many years and never had to machine when the right part was bought.
Maybe there are doing something different? But the set that I just bought last week worked fine with stock rods.
I was only talking about the 408ci pistons- the regular ones use stock pistons -(from Keith Black webpage "Use Magnum rods or regular 360 rods with small end narrowed to Magnum rod width(1").")