The NP421c, sounds like a good substitute.
I have found an adapter to the transfer case of the land cruiser(From the allison). In the adapter a speed sensor is used to go to the ecm, the toyota speed sensor on the rear of the transfer case is then used to drive the cruiser speedo. Would this mean the Allison will have problems shifting when put into 4X4 lo? How could this be rectified?
Also in regards to making the tach work on the cruiser cluster (it's looking easier now to maintain the cruiser cluster) I have found a commercial converter, for all tach types. Its called a Dakota Digital Tach adapter.
Cheers
You can swap in a 261/263 input shaft into a 241 transfer case, and the bolt pattern is the same. if you put the speed sensor before the transfer case, then you simply leave out the 4 low signal wire to the ECM/TCM, and all is well.