I guess I never came back and posted my findings. I was right.
In 1974-1975, all K series trucks (K10 Blazer, Suburban, and pickup along with K20 Suburban and pickup) came with an NP203 if they were ordered with a V8 engine. Six cylinders in ‘74-‘75 did not get an NP203, even with an automatic. Oddly, only the K20 pickup was available with a six cylinder in 1975. All 1975 K10 Blazers, Suburbans, and pickups came standard with a V8.
I have found 1975 SPID’s where the truck was ordered with a V8, and optionally ordered with an NP205, but the NP205 had to be ordered specifically, otherwise the truck would have come with an NP203.
So the answer is 1974-1975 V8 equipped trucks.
Martin