Just going off what year and application the trans is, it's most likely an NP241.
One more option you could do, check out Advance Adapters. You should be able to get the proper adapter for the 5 speed to allow you to use the older passenger side drop 'cases, as i don't think any of them was used with that trans factory. If you do change the 'case, being a 1 ton truck, I would suggest the NP205. By going to the RH drop, that will open up a much broader selection of axles, as you could use pretty much any GM or Dodge leaf spring front axle.
