If you have a driver side drop it will not be a NP205.
The 4L80E/NP205 was offered one year only in the V3500 1 Ton Chevy GMC 4x4.
I've read write ups on the conversion with the computer and harness being the major expense of the conversion.
I bought one in a V3500 Crew Cab a few years ago in a govt auction specifically for the drive train and later had to sell it for financial reasons.
They are out there but not as common as you think.
Here is what to look for in the cab to determine the 205 from a glance: (notice the straight shifter stick in the center floor)
Here is the rare as hens teeth adapter:
