PART NO.  SPL.PAGE  DESCRIPTION                                                           
ARH120    15.C.1    Radiator block assembly -(cooling system, 1500) -was ARH61 -
    -(early change point unknown, but shows in SPL Issue 2- February 1960)
ARH120    16.C.1    Core assembly -radiator -(cooling system, 1600)

The MGA service parts list issue 1 (green book) lists the radiator part number as ARG61. The second edition (Issue 2- February 1960-yellow cover) lists the part number as ARH120. The 1600 and 1600-MK-II (SPL issue 4) also list it as ARH120. Why the radiator part number was changed early in 1500 production is not known (yet).

Also see MGA Part Numbers - ARH61
and Original Radiator for the MGA - CO-100