Yep, NP205 was the only option in GM trucks in 1980.
1979 was the last year for the NP203 option, 1981 was the beginning of NP208's, so 1980 is an unusual year where there is only one transfer case available (NP205). You could get an NP205 as an option in any of the 70's GM trucks and in most of the 81-91 1 tons.