77 Chevy C-30 Transfercase Questions?

[77wells]

Hi, I have a 1977 C-30 with the turbo 400 and a np-203 transfercase. My transfercase needs to be rebuilt, so I am looking for some input from others who know more about these. From what I can find, I can rebuild this one and keep the full time four wheel drive, or I can convert it to a 2lo 2hi N 4hi 4lo. I would imagine your tire wear would be better and your mileage might increase a bit?? What are the ups and downs of the two? Also I found that you could put a np-205 in it. To my understanding these are 100% gear driven cases? These would be heavy duty but would it make more noise and take more power? Also you need and adapter for this? I plan on putting a built 454 in the truck down the road, right now it has a 350 and I use it to pull trailers and haul wood, so its under fairly heavy loads alot of the time. Any input would be greatly apprecitated! Thanks!