I didn't find the burial place for either one but I did find a lot of info as I was searching. Also there are a couple of Zebulon Alphin's. Yours was born about 1920 in Kentucky. There is another Zebulon Alphin b. abt. 1932 in KY who also lived in Idaho.
Name: Zebulon Alphin
Spouse: Zeruiah Childress
Married: 3 Dec 1840, Lee County, Iowa
Source: RootsWeb, http://userdb.rootsweb.ancestry.com/marriages/cgi-bin/marriage.cgi?..http://userdb.rootsweb.ancestry.com/marriages/cgi-bin/marriage.cgi?...
In 1850 the family was living in Wayne, Iowa.
Zebulon Alphin, b. KY, 30, farmer.
Zeruiah, wife, b. KY, 25.
Luke, b. IA, 7.
Nancy J., b. IA, 4.
William B. b. IA, 2.
In 1856 the family was living in Medicine, Wayne, Iowa.
Zebulon Aulphin [how indexed], b. KY, 36, farmer.
Zeriah, wife, b. KY, 31.
Luke P., b. IA, 13.
Nancy J., b. IA, 10.
W. B., son, b. IA, 7.
Kenian, dau, b. IA, 4.
James F., b. IA, 1.
Source: Iowa State Census Collection 1836-1925.
In 1860 the family was living in Clinton, Wayne, Iowa.
Zebulon Alpine [how indexed], b. KY, 40, farmer.
Zera, wife, b. KY, 30.
L. P., son, b. IA, 17.
N. J., dau, b. IA, 14.
W. B., son, b. IA, 12.
Kesiah, dau, b. IA, 9.
J. F., son, b. IA, 5.
Thomas, b. IA, 2.
Sometime after 1860 Zebulon and Zeriah divorced.
In 1870 Zebulin was living in Upper Payette Valley, Boise, Idaho Terr.
Abraham Smith, head, b. MO, 35, farmer.
John Lee, b. Ireland, 25, farm laborer.
Zebulin Allfin, b. KY, 50, farmer.
Three others who aren't related too.
Name: Zebulon Allfin
Bride: Edith Starr
Married: 2 June 1877, Ada Co., ID
Source: Brigham Young University-Idaho, Vol. 1, p. 142.
In 1880 he Eda were living in Payette Valley, Ada, Idaho.
Zepp Allfin, b. KY, 60, farmer.
Eda, wife, b. KY, 50.
William Patterson, boarder.
Ole Holverson, boarder.
I searched Ancestry, FamilySearch, Idaho Death Index and Idaho Digital Archives and didn't find any death info for either one.
You mentioned he was back in Wayne Co., IA in 1900 but couldn't find that in the Census info either. I think that because he lived there when he was 80, he and Eda/Edith died there.
I'd post my query in that county.
I found his wife Zeriah living in 1900 in Howard, Wayne, Iowa with their daughter's family.
Ulrick Chapman, b. OH, 56, July 1843, farmer, marr 24 yrs.
Shara H., wife, b. IA June 1861, had given birth to 11 children and all alive in 1900.
Robert E., b. IA, Sept. 1883, farm laborer.
George W., b. IA Sept. 1885, farm laborer.
Nancie K., b. IA, Aug 1887.
Earl, b. IA Sept. 1889.
Ralph L., b. IA May 1892.
Sarah N., b. IA, July 1894.
William E., b. Aug 1896, IA.
Ruby K., b. Dec 1899.
Zeriah Allphin, motherlaw, b. KY, Jan 1826, widow, gave birth to eight children and five alive in 1900.