I will break with tradition here.
I am just getting my M151 to the mechanical state I generally keep all my vehicles in (I maintain to a very high standard). I have driven mine a good bit on the road now and I would not hesitate one bit to take mine on a 300 mile trip. In fact, I plan to do just that at least 3-4 times per year with it. I do not however plan to do it on the interstate and where possible, I'll be tied in with other trucks in a self supportable convoy. (M151s catch rides in deuces quite easily)
Like I said, no doubt in my mind that mine could do it. No doubt in my mind that mine will do it.
That said, that peace of mind comes from changing:
100% of the propeller shaft joints (all if mine had some visible wear)
100% of the drive shaft u-joints (all of mine had some visible wear)
50% of the wheel bearings new, the other half cleaned and greased.
Rebuilt steering gear.
All diff leaks fixed, full POL change, running synthetic oils in gear cases.
In tank rotary fuel pump conversion.
It was a long road to getting back to "deployable" condition. If you do not know the history on the one you are getting, I would trailer it. A tow dolly is an option ONLY of you take the time to remove the propeller shafts on the axle that is on the ground. You do not want a failed U-joint back there fragging on you and tearing things up on your new prize.
For cruising speed, mine comfortably runs 60 which I consider a minimum to keep up with the Deuces and can dart up to 70-75 for occasional sprints but I do not push it. Noise/comfort is not great but it is not much worse than any other military truck.