Politically: Maybe not quite what you are looking for, but I looked on Wikipedia, and found this. Looks like there was a conflict in 1965, which was fought because of the Kashmir conflict. Nanga Parbat is located in one of the Kashmir provinces, so there is going to be tension in 1970 (and today) that was not there in the 1930s (due to British rule). If the players are Anglos (and obviously not Indian or Pakistani), it is probable that they may not notice many problems, but there will inevitably be difficulties if they hire any sherpas.
1930s: IIRC, There wasn't much that was done then that is done now. For example, people did not use safety harnesses. If they WERE using a rope, it go from the top of the rope (uphill side), to the hand, over the shoulders and down the front of the climber, then between his legs, and then dangle down the cliff. Also, there were no synthetic materials. You kept warm by layering on many layers of wool and rubberized canvas to cut the wind. People did not know about the dangers of hypoxia and didn't use oxygen tanks. Pulmonary Edema was a MAJOR danger.
1970: Safety harnesses were used, but to make one, you took a piece of webbing about 10 feet long and folded in half. Put 1 foot or so from the loop in front of you, and the rest through your legs. reach around and hook the tails in the loops and then wind back around and finish by knotting the two tails off. Take a metal D-link and thread through the original loop and the knotted tails. Then you take a figure 8 link and pull the safety rope through the bigger loop and hook over the smaller loop. Clip the small loop into the D-link on your harness, and you are ready to climb. You also have access to nylon windbreakers (much lighter than rubberized canvas), and oxygen tanks. Sherpas help carry all the junk to the basecamps, and help climbers out by caching O2 tanks up the mountain (and stringing safety lines). You also have much more availability of things like crampons and ice axes.
today: you put on a safety harness much like a pair of shorts. There is something like a belt that you clip on, and attached to this belt are strings that connect to loops that go around your thighs. There is a small metal loop that you clip the D-Link to the metal loop. Connect the figure-8 to the safety rope and clip to the D-ring like in the 1970s. There are also now many synthetic fibers. For example in 1970, you wanted a lightweight sleeping bag that would keep you warm? You wanted down. Get down only a little wet, and it would not insulate you at all. Now there are fibers that don't lose their loft when wet, so they keep the person inside warm.
Timeless advice: Altitude sickness is when the body is used to one altitude (say sea level) and is subjected to a significantly higher elevation (say 10,000 feet, don't laugh I personally suffered this difference). According to wikipedia, you can acclimate to an altitude by multiplying the elevation (in kilometers) by 11.4. Were I one of your players, I'd go chill in the town of Chilas which looks to be less than 50 miles from the peak. I would go and acclimate (as a total outsider, I'm guessing it's around 6500 meters). Based on my scientifically guessed numbers, that means about 75-80 days acclimating. The logistics of getting gear, food, whatever is needed to purge the mountain of the evil left by Merkl, etc. would probably take up a good chunk of that time. Maybe take a leisurely trip to the base of the mountain (taking up a few days to get muscles used to working in the elevation, and more time to acclimate). from the base of the mountain, take a day off to rest (and yet another day of acclimation), then take off for the summit. Since Nanga Parbat is in the Death Zone, the players will need either plenty of oxygen, or be able to get the job done and below 8000 meters quickly (all my google-fu failed me in finding out how long one can survive in the Death Zone).