UIM OE was basically the same as what we in North America called MOD 50, at least that is what we called it here in Canada from about 1975 until it kind of became SST 60.
Lars can tell you more about the variuos OMC models in OE, the Merc MOD 50 models were the 650X then the 700X. In Canada we were allowed to use the Merc 650XS in our SE class.