The first thing is, what kind of base shape are you in now? The primary thing you need to consider is taking it slow and acclimatizing. With the 3 days you're allowing, this should be plenty. What type of mountain experience do you have? Gear? Knowledge of weather and signs of AMS? Many of those things are more important than what shape you're in....that's the main reason I'm asking. Your conditioning affects your ability to make it to the top.....those other things allow you to stay alive.
I'm kind of a conditioning nut, but I do some unconventional things. Here is a sample of my typical training week. Please keep in mind that I'm also an alpine wall climber so I've tailored this for upper body work as well. For a moderately strenuous hike like Whitney and a lot of the 14ers, the upper body work isn't necessary. Also, the amount of weight used in these movements purely depends on what you can handle.....work up to this slowly if you're in average to slightly below average shape. I'd recommend 4 weeks of general cardio and light weights to get your body used to movement and handling the load, before getting into more strenuous power and endurance training. The last thing you want is to hurt yourself.
Monday- 45mins on indoor climbing wall
30mins strength -- Chest/Back
45mins stairmaster
Tuesday- Step ups with loaded barbell/pack. I setup two heavy metal steps, one 18" the other 24", I walk up both and then back down it. Then I do the 18" laterally. I do this with 120lbs on the barbell, but the weight is subjective. I do 6 sets of thirty. I do the lateral movement to simulate scrambling on scree with a heavy pack. I also do these in intervals. One set will be slow and methodical, the next set will be borderline sprinting.
20yd sprints pulling/pushing 150lb sled. Again, the weight is subjective. I do this down and back four times, take a 45second break, and then do another set. 6 sets of these. Great for conditioning the lungs for high exertion.
Then I do 30mins on the incline treadmill doing intervals. 5 mins on max incline at 3.5mph, and then 1 min at max incline at 6mph.
Climbing wall
Wed- Biceps, triceps, shoulder weight training.
45 mins stairmaster
Sprint intervals on indoor track
Thurs- Same as Tuesdays workout
Fri- Leg weight training. Leg press, squats, calf raises, lunges, step ups.
45mins rowing
45 mins stairmaster
Sat- Rest/casual biking or hiking
Sun- Total rest
You can also bike/swim for cardio conditioning, but those exercises don't quite prepare your body in the same way for hiking up hill with a loaded pack. The best exercise is to hike uphill at altitude with a loaded pack, but that can be harder to do due to time constraints/work/family. Everyone is different, just find something that works for you. The best thing to do is have a target goal to track your progress. Find something that really wears you out and test yourself on that activity every 2 weeks. Write down how you felt 2 weeks ago, and then compare it to your current results. This way you can see what areas you're really progressing in, and which need some more work. A good example is finding a long hilly hike/mountain nearby. Hike it with a 10lb pack and see how you feel. Write down how your calves, hamstrings, quads, back, and breathing felt during this test. Then after 2weeks of training, go back and compare. Again, write down how you feel. If you notice you're lagging in a certain area, focus your workouts to target that area. I noticed my calves were lagging behind in terms of conditioning, so I started doing more weights and other movements to target them. I went back after two weeks and noticed a huge improvement in how they felt. It's all about keeping your muscles in balance as imbalances can lead to injury.
Nutrition is extremely important. Make sure you're getting lean protein. Eat a lot of leafy greens and veggies. Carbs are very important. Stay away from white processed flour and artificial sugars. Focus on getting your carbs from whole grains, fruit, oatmeal, etc. DRINK ALOT OF WATER. It's estimated that 70% of Americans walk around partially dehydrated every day.
I hope this helps....I know it was long.