[Gav]

I will go out on a limb here and say that there is no difference.
The LS6 was just a hotter version of the LS1.
The LS6 had better heads, more compression, internally the block was a bit different, a slightly larger cam, bigger injectors and the LS6 manifold.
The LS6 intake later became standard on all LS1s.

Could have been different but I doubt it. Just had a flick through a couple of books and neither meantion a different starter.

Maybe the truck starters are different?