there are 2 different 205 cases. one has a round 6 bolt mounting pattern. this one will bolt to your current adapter. The other has a 8 bolt pattern shaped like a peanut. to use this one you will need a new trans to t-case adapter.
Either t-case you use you will need to figure out your tailshaft. 205's came with different inputs. 10 spline from behind a stick, and a higher spline counts from behind the automatics.
You will need two new driveshafts. a 205 could have a slip yoke rear or use a yoke and a slip in the shaft. On the front output it could be a flange or a yoke.
You will need to figure out your shifters also. The 205 uses a bolt into the adapter housing to hold the shifter.
Keep in mind that your current 208 has a 2.72:1 low ratio. a 205 will 1.98:1. which means you will have less reduction offroad.
What was the hope in switching t-cases? were you looking for more strength? did you blow up the 208 and have a 205 laying around?