I checked the Washington County History Book and asked around, but have found no Walker plantation. No word of anything resembling a plantation just south of town in 1862, and no Walker family in that spot. There were Walkers a bit further north -- if you have names, I'll be happy to look for them. You might also call the Shiloh Museum, (501) 756-8165. The folks up there are very knowledgeable. They don't do genealogical research, but they might have heard of the Walker plantation and know where it was.