The Amateur journal says, "Each of the four edges are equal to the plaque's first and seventh numbers side by side." So what are the first and seventh numbers on the plaque?
The first date is 1866; further down, it says May 4, 1895. So the first number is 1, the seventh number is 8, and side by side they make 18. So you need to arrange the numbers on the door so each side adds up to 18.