Also, a GMT900 truck with 6.2 I've read also has the 6 lug pattern on a 14 bSF...with disc already, LOL. Although that is obviously not a direct plug and play swap and those will most definitely have numerically lower gear rations since they came with 6 speed tranny. Also, that was not a cheap option on those trucks, just the really high trim trucks, so won't be easy to source either... read: not worth it.
On the 6 to 8 lug adapter option, some guys run some spacers just to increase the rear track width since the rear on these trucks was narrower than the front. Won't the lug adapters basically do the same?