Kertau (RSO) - EPSG:4751

WKT

GEOGCS["GCS_Kertau_RSO", 
	DATUM["D_Kertau_RSO", 
		SPHEROID["Everest_Modified_1969", 6377295.664, 300.8017]], 
	PRIMEM["Greenwich", 0.0], 
	UNIT["Degree", 0.0174532925199433]]

WKT2

GEOGCRS["GCS_Kertau_RSO", 
	DATUM["D_Kertau_RSO", 
		ELLIPSOID["Everest_Modified_1969", 6377295.664, 300.8017]], 
	PRIMEM["Greenwich", 0.0], 
	CS[ellipsoidal, 2], 
	AXIS["Latitude (lat)", north, 
		ORDER[1]], 
	AXIS["Longitude (lon)", east, 
		ORDER[2]], 
	ANGLEUNIT["Degree", 0.0174532925199433], 
	ID["EPSG", "4751"]]

Data from @esri/proj-codes

{
  "wkid": 4751,
  "latestWkid": 4751,
  "macro": "PE_GCS_KERTAU_RSO",
  "name": "GCS_Kertau_RSO",
  "wkt": "GEOGCS[\"GCS_Kertau_RSO\",DATUM[\"D_Kertau_RSO\",SPHEROID[\"Everest_Modified_1969\",6377295.664,300.8017]],PRIMEM[\"Greenwich\",0.0],UNIT[\"Degree\",0.0174532925199433]]",
  "wkt2": "GEOGCRS[\"GCS_Kertau_RSO\",DATUM[\"D_Kertau_RSO\",ELLIPSOID[\"Everest_Modified_1969\",6377295.664,300.8017]],PRIMEM[\"Greenwich\",0.0],CS[ellipsoidal,2],AXIS[\"Latitude (lat)\",north,ORDER[1]],AXIS[\"Longitude (lon)\",east,ORDER[2]],ANGLEUNIT[\"Degree\",0.0174532925199433],ID[\"EPSG\",\"4751\"]]",
  "description": "Kertau (RSO)",
  "authority": "EPSG",
  "version": "6.5(10.0.0)",
  "deprecated": "no",
  "areaname": "Asia - Malaysia (west) and Singapore",
  "extent": {
    "slat": 1.13,
    "nlat": 6.72,
    "llon": 99.59,
    "rlon": 104.6
  }
}