Sorry brother for late reply..but was posted in remote naxal district for conduct of LS elections, and then somehow missed this post tag
For LTC to Tawang, after taking flight to Itanagar only option is ASTS online booking of Xylo/Cab, because govt doesn't accepts Bills of private cabs/taxis/buses.
Alternatively, may claim bill only upto bhalukpong and then can take private cab from there( fare can not be claimed)