Have you checked to see if the NP205 is a round 6 bolt or figure 8 style? I'm thinking 83 would be figure 8 but...
The later TC is most likely a round pattern.
If you have, or can locate a round pattern 205, it may bolt up, or almost bolt up. The round pattern TCs use an ANSI standard round pattern with one bolt hole slightly offset. The thing is, different TCs have that offset hole at different spots--even within GM
