What year your air cooled Volkswagen engine is the engine number is AD226815X?

i dont know of any engines that started with AD

however

type1

AE 1971/72 1600cc - dual relief, dual port AH 1973/74 1600cc - 8mm head studs with case savers AJ 1975-1979 1600cc - fuel injected type2

AW 1973/74 1800cc - dual carb. AW 1975 1800cc - fuel-injected AP 1974/75 1800cc - European only

type 3

AN 1974 1800cc - 8.6:1 compression AT 1974 1800cc - European only, dual carb.