The 5.3 with the H3 Transfer case does work, but you need to re do the drive shafts for length. From what I have seen and read and looked at in order to keep the A/C for the 5.3 it would require a custom A/C kit and the price would increase greatly. This also get rid of TOD and that is something that I am wanting to keep in the VX.
The AR5 Transmission should bolt up without much of an issue to the NorthStar from what I have read. This si not something that I have researched in depth but from what I can tell it should be just like the 4L30E. The reason why I have not looked into this is because of the cost for the conversion. I am trying to keep the cost down as much as possible because like many others I have a hard time putting more into the car than it is worth, even though I have no plans to ever sell it.
If there is a lot of interest in swapping the stock auto with the AR5 Manual transmission I am sure we can figure something out. This would be able to keep the TOD as well as having a very stout transmission