Well, I'll chime in with the usual suggestions.
203 is a chain driven case, 205 is all gear. 205 is going to be more durable in the long run.
A 205 swap requires the crossmember, adapter, coupler, shifter, and driveshafts. Some would say to go ahead and do a doubler (203 range box and 205 transfercase mated together with an adapter plate), but that is a decent amount of $$.
I personally saw no reason to spend any money on my 203 (part time kit or whatever), but I also needed a new driveshaft so I knew I was going to have that expense. There are 2 types of part time kits out there, one is just a couple of gear inserts into the output differential, and the other is an actual replacement rear output shaft. Check em both out before buying.