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I have the two Advanced Adapters components (kit) that sound like your description...
50-5302 : GM NP205 Aluminum Stock replacement adapter housing for TH350 transmissions 6273963
50-5304 : Hybrid coupler sleeve for GM NP205 transfer cases. Coupler has 27 spline transmission to 10 Spline Transfer Case
About $450 total from Advanced
I'll sell for $350 plus fees and ship.