Chestnuts are primarily wind pollinated, not insect pollinated. That means they need to be in pretty close proximity. Trees a hundred or two yards apart are functionally sexually isolated. There is a tradeoff and different folks use different strategies. One strategy is to plant them as close as possible such that they are far enough apart not to compete for resources when fully grown. Of course with this strategy the crowns are close for pollination at full size but pretty far when young. The strategy I'm using is to plant them much closer. Some orchards use this strategy as well. I presume that some trees won't survive. When adjoining trees survive, they will have higher production when young because of the increased pollination. When they begin to compete for resources, I'll simply keep the best tree and cull the competing tree. By then, the best tree will produce more nuts than the combination as it gets more resources.
I'm a bit reluctant to give a specific distance. Chinese chestnuts tend to be low growing and have wide spreading crown while American chestnuts tend to grow straight and tall. Dunstans are hybrids. Some seem to take on more of the early branching Chinese form and others seem to take on more of the taller American form. I can't tell you what you should do, but I'm happy to share what I've done. I'm planting mine with a spacing of about 18'.
Thanks,
Jack