Here is the chronolgy of T-cases.
73-79, majority came with the NP203. Fulltime case, 2.01:1 low range chain driven with a cast iron case
73-80, NP205, mostly behind the SM465 4 speed. It was the only T-case offered in 1980 and came behind all trannies. 73-79 versions were fixed yoke, 80 was slip yoke. 1.96:1 low range, gear drive and cast iron
81 saw the introduction of the NP208 which came behind all available trannies. It was chain driven, aluminum case, 2.61:1 low range with a slip yoke output. It was replaced with the 241 in 89. The 241 is similar to the 208 but has a 2.72:1 low range. It is also slip yoke output but a slip yoke eliminator is avaialble through the aftermarket. 89-91 241's were found behind every available tranny also.
Hope that helps some!
Rene