I would not be afraid of the NP203 t-case, my 1975 Ford F-250 has had one from day one and has never broke. The last 3 years as a sled puller. I have put a bearing kit in it twice, the last time both sprockets and chain. I have seen the 205's break regular in the sled pullers, usually the in-put shaft. As far as chain drive, they all have chain now. The low range box of the 203 is tough.
Nick