The Beogram has a five pin DIN plug because there wasn't sutch thing as datalink in the early seventies
The two extra pins are for conunicating with a datalink compatiple turntable, e.g. Beogram 8002. This means that you can't remote control this unit, or any other 400* series with your Overtoure, but the beogram will work anyway and send sound to your BeoSound via the 5-pin DIN.
Beocenter 9300, Beogam CD50, Beocord 5500, Beomaster 3400, Beomaster 4400, 2 Beogram 4000, Beomaster 8000, 2 beogram 8002, Beovox S-75, Beovox MS150.2, Beovox RL6000, Beovox S-35, Beomaster 6000, 2 Beocord 9000, Beocord 8004, Beocord 5000, Form 1, 2x Beolink 1000, Beo4, MX3500, LS4500. Born 1993.