The K-36 is a bit lighter than the newer 2157, and much lighter than the current 1969 Saturns. I'm old enough that I regularly flew the K-36 on a D13-3 or D12-3. That being said, I did lawn dart one when it either had a bonus delay or sub-par thrust .

An Aerotech E gives a lot more margin than a D - although I'd stick with an E15 or RMS E18-4W (I used to trim the delay grain down a bit for a shorter delay when I used an E18-4W). I like the White Lightning propellant in a Saturn V, and as noted it looks better a bit slower.
But don't fly an Estes Saturn V in strong or gusty winds - it can easily cause it to go unstable.