Fao 1979 - ESRI:105791

WKT

VERTCS["Fao_1979", 
	VDATUM["Fao_1979"], 
	PARAMETER["Vertical_Shift", 0.0], 
	PARAMETER["Direction", 1.0], 
	UNIT["Meter", 1.0]]

WKT2

VERTCRS["Fao_1979", 
	VDATUM["Fao_1979"], 
	CS[vertical, 1], 
	AXIS["Gravity-related height (H)", up, 
		LENGTHUNIT["Meter", 1.0]], 
	ID["Esri", "3886"]]

Data from @esri/proj-codes

{
  "wkid": 105791,
  "latestWkid": 3886,
  "macro": "PE_VCS_FAO_1979",
  "name": "Fao_1979",
  "wkt": "VERTCS[\"Fao_1979\",VDATUM[\"Fao_1979\"],PARAMETER[\"Vertical_Shift\",0.0],PARAMETER[\"Direction\",1.0],UNIT[\"Meter\",1.0]]",
  "wkt2": "VERTCRS[\"Fao_1979\",VDATUM[\"Fao_1979\"],CS[vertical,1],AXIS[\"Gravity-related height (H)\",up,LENGTHUNIT[\"Meter\",1.0]],ID[\"Esri\",\"3886\"]]",
  "description": "Fao 1979",
  "authority": "Esri",
  "version": "10.0.0",
  "deprecated": "codechange",
  "areaname": "Iraq - onshore",
  "extent": {
    "slat": 29.06,
    "nlat": 37.39,
    "llon": 38.79,
    "rlon": 48.61
  }
}