I can't tell you how many times this topic has been discussed. I bet you will find a minimum of two threads, but most likely more if you conduct a search. One thread recently covered the highest mileage deuces that are known. Another asked how many miles could one expect out of a multifuel motor (that thread was repeated at least twice). Yet another asked how robust the motor was...and how long it would last before requiring a complete overhaul. No offense intended, but, if you think the topic you are asking about is one that could have been covered before, please do a search.
Now, to answer your question...it has been correctly stated above...there is NO way to tell how many miles you'll be able to get out of your truck. Most military trucks have fewer than 30K miles on them...with very few until recently showing more than 40K or 50K miles. The highest mileage deuce that I've seen had over 90K on the odometer. If you take care of it, it should last. Hopefully, it has not been abused so far during its life. With all this said, other threads have concluded that you will most likely NOT get a few hundred thousand miles out of the motor like other medium or heavy duty diesels.