The 55 amp AL74X can be either internal or external regulator. Mine is external. I replaced my fender-mounted original regulator with a more modern 280SL regulator that looks the same as the 230SL regulator. I wanted the car to look pretty close to original.
The connectors on the AL74X are completely different than the original 35 amp alternator (which had no connectors originally, although the newer 35 amp alternator does have connectors, apparently). Although the connectors on the AL74X are different than the old 35 amp alternator, the "CONNECTIONS" are the same - DF, D-, D+, B+ and Ground (frame to mtg. bracket). It's just necessary to re-terminate the wires with two new connectors.
I don't remember how to rewire the harness for an internal regulator alternator. I would have to study it again.
Tom Kizer