I am familiar with single side nocks but I've never seen any like this. Where did you get this design?
To me, they are set up for disaster. The tips are too thin and wide and the depth and shape of the nocks lends itself to splitting the grain apart and especially with so much draw weight. Thicker, narrower tips would work better, IMO. Look at the English war bows. Their tips are at least 1/2"x1/2" and even with a single side nock the nock holds the string without that deep of a nock. The weight of the bow will keep the string in the nock.
After thinking about it I think I would add overlays and underlays and even a wrap over them to insure that the tip design will hold up to that much weight.
That buff horn will work but don't you have something available so you don't have to order water buffalo horns. Deer antler, bone, goat horn, etc. Check out Pet Smart or other similar pet store for dog bones, etc that would be appropriate.
Where did you get that design?