Have you contacted the Hill Co. Genealogy Society in care of the Hillsboro City Library, 118 South Waco St., Hillsboro, TX 76645, telephone 254-582-7385?
On findagrave.com, Hiram Walker is shown buried at Prairie Valley Cemetery. Directions have a big error. It states use state hwy 933 south from Whitney. Wrong. Go southwest from Whitney on State Hwy 22 which goes over the dam of Lake Whitney on the Brazos River. A little over half way between Whitney and the dam, FM (farm to market road) 2960 begins, going south. If I remember correctly, 2960 is only a few miles long. Don't remember just where 2101 intersects, but remember the cemetery is adjacent to the Prairie Valley church. There is no direct road connecting the area to Aquilla. Laguna Park, on the west end of the dam, did not exist until about 1951 when the dam was built.
Again, contact the gen. society as they or a member of their society might have information to help you. Good luck.