On the first part, I don't believe Numerology, Astrology or any other tool for that matter gives hints to when or how we'll die. When you look into the Pinnacle and Challenge at the time of his death, you get insight into the area of lessons for the 8 years of his 3rd cycle. Then, you have different sub-flavors brought by the personal years and essence every year, then you have an extra layer with personal months... It all dwarfs the moment of his death in terms of duration and again, the point of charts is to offer us guidance into how to make the best of our potential and look out for pitfalls. The rest is trifles.

I'm also not getting the same numbers as you for his Challenge and Pinnacle.

First Pinnacle: sum of your month and day of birth
Second Pinnacle: sum of your day and year of birth
Third Pinnacle: sum of the 1st and 2nd Pinnacles

with 05/29/1917, we get
First Pinnacle: 7
Second Pinnacle: 2
Third Pinnacle: 9

For Challenges:

First: result of subtracting your month from your day of birth or vice versa
Second: result of subtracting your month from your day of birth or vice versa
Third: result of subtracting your First Challenge from your Second Challenge or vice versa

You should get 4 for the cycle in which he died

A 9 Pinnacle and 4 Challenge sound pretty relevant with his actual life. 9 if for connection with groups of people, and when positively expressed, with uplifting purposes. The 4 challenge is that of the builder, learning to build foundations, acquiring resilience, focusing on details, etc... It matches his campaign years and the first years of his presidency.

On the second point, you have a very good point when noticing some similarities between 4 and Cancer. They do not equate each other though. 4 has very dry and uneffusive vibes, while cancer is strongly associated with emotions. One reason you can't have a direct correlation is you have only 9 numbers and 12 signs/Houses. What you can do pretty accurately though is describe Signs with a combination of numbers or the other way around. For example, you can see Cancer as a blend of 4 and 2... Or 6 as a combination of Virgo for the health/service traits and Libra for the artsy/aesthetic skills. You can find similar correspondences for every sign.