AGD 1966 AMG Zone 56 - EPSG:20256

WKT

PROJCS["AGD_1966_AMG_Zone_56", 
	GEOGCS["GCS_Australian_1966", 
		DATUM["D_Australian_1966", 
			SPHEROID["Australian", 6378160.0, 298.25]], 
		PRIMEM["Greenwich", 0.0], 
		UNIT["Degree", 0.0174532925199433]], 
	PROJECTION["Transverse_Mercator"], 
	PARAMETER["False_Easting", 500000.0], 
	PARAMETER["False_Northing", 10000000.0], 
	PARAMETER["Central_Meridian", 153.0], 
	PARAMETER["Scale_Factor", 0.9996], 
	PARAMETER["Latitude_Of_Origin", 0.0], 
	UNIT["Meter", 1.0]]

WKT2

PROJCRS["AGD_1966_AMG_Zone_56", 
	BASEGEOGCRS["GCS_Australian_1966", 
		DATUM["D_Australian_1966", 
			ELLIPSOID["Australian", 6378160.0, 298.25]], 
		PRIMEM["Greenwich", 0.0], 
		CS[ellipsoidal, 2], 
		AXIS["Latitude (lat)", north, 
			ORDER[1]], 
		AXIS["Longitude (lon)", east, 
			ORDER[2]], 
		ANGLEUNIT["Degree", 0.0174532925199433]], 
	CONVERSION["Transverse_Mercator", 
		METHOD["Transverse_Mercator"], 
		PARAMETER["False_Easting", 500000.0], 
		PARAMETER["False_Northing", 10000000.0], 
		PARAMETER["Central_Meridian", 153.0], 
		PARAMETER["Scale_Factor", 0.9996], 
		PARAMETER["Latitude_Of_Origin", 0.0]], 
	CS[Cartesian, 2], 
	AXIS["Easting (X)", east, 
		ORDER[1]], 
	AXIS["Northing (Y)", north, 
		ORDER[2]], 
	LENGTHUNIT["Meter", 1.0], 
	ID["EPSG", "20256"]]

Data from @esri/proj-codes

{
  "wkid": 20256,
  "latestWkid": 20256,
  "gcsWkid": 4202,
  "macro": "PE_PCS_AGD_1966_AMG_56",
  "name": "AGD_1966_AMG_Zone_56",
  "wkt": "PROJCS[\"AGD_1966_AMG_Zone_56\",GEOGCS[\"GCS_Australian_1966\",DATUM[\"D_Australian_1966\",SPHEROID[\"Australian\",6378160.0,298.25]],PRIMEM[\"Greenwich\",0.0],UNIT[\"Degree\",0.0174532925199433]],PROJECTION[\"Transverse_Mercator\"],PARAMETER[\"False_Easting\",500000.0],PARAMETER[\"False_Northing\",10000000.0],PARAMETER[\"Central_Meridian\",153.0],PARAMETER[\"Scale_Factor\",0.9996],PARAMETER[\"Latitude_Of_Origin\",0.0],UNIT[\"Meter\",1.0]]",
  "wkt2": "PROJCRS[\"AGD_1966_AMG_Zone_56\",BASEGEOGCRS[\"GCS_Australian_1966\",DATUM[\"D_Australian_1966\",ELLIPSOID[\"Australian\",6378160.0,298.25]],PRIMEM[\"Greenwich\",0.0],CS[ellipsoidal,2],AXIS[\"Latitude (lat)\",north,ORDER[1]],AXIS[\"Longitude (lon)\",east,ORDER[2]],ANGLEUNIT[\"Degree\",0.0174532925199433]],CONVERSION[\"Transverse_Mercator\",METHOD[\"Transverse_Mercator\"],PARAMETER[\"False_Easting\",500000.0],PARAMETER[\"False_Northing\",10000000.0],PARAMETER[\"Central_Meridian\",153.0],PARAMETER[\"Scale_Factor\",0.9996],PARAMETER[\"Latitude_Of_Origin\",0.0]],CS[Cartesian,2],AXIS[\"Easting (X)\",east,ORDER[1]],AXIS[\"Northing (Y)\",north,ORDER[2]],LENGTHUNIT[\"Meter\",1.0],ID[\"EPSG\",\"20256\"]]",
  "description": "AGD 1966 AMG Zone 56",
  "authority": "EPSG",
  "version": "7.8.2(3.0.1)",
  "deprecated": "no",
  "areaname": "Australasia - Australia and PNG - 150~E to 156~E",
  "extent": {
    "slat": -46.44,
    "nlat": -2.32,
    "llon": 150,
    "rlon": 156
  }
}