Does the official Army Workout Plan work?

I would be at a point where you can safely ruck a 35 lb pack well under the three hour time limit. I would also suggest you be at a point where you have been carrying a heavy ruck 50-75 pounds - at a strolling pace for at least two hours straight every week, for six months; at that point your tendons, ligaments and connective tissue will be strong enough to endure the muscle wasting you will experience. Muscle is nothing in Ranger School. All your fat and muscle will be gone halfway through. You need long term lean strength

Any workout plan will work as long as you are committed to it and grind hard to the fullest. Workout plans work based upon the effort a person put into it. So results will depend on your effort.

Not sure, I didnt train up. I would focus on stamina for sure and carrying loads. Dont over train. That can and will happen if you go too hard.

It does work, or they wouldn't put it up there. There are also a bunch of other plans out there that either cater directly to Ranger School, or a ruck based selection that would work.
I recommend training for 2 months on whatever plan you pick, then get to your posts Small Unit Ranger Tactics (SURT). Those that go to SURT have a much higher chance of getting through Benning, which increases your chances of graduating becasue thats where most people fail out. The stats of what people fail is also on the website.

If you overtrain, you're less likely to make gains and more likely to injury yourself. The plan is a decent base, but we're all individuals. Your plan should be focused on passing all the RAP week events and being able to carry a ruck for extended periods. After RAP week, there are no other formal physical assessments, you just have to be able to haul a heavy pack through the sand, mountains, and swamps.