I'm investigating the same problem. I believe there's a 70 Watt unit out there that has the same connector. I was trolling around the yard the other day and noticed some with double pulleys and assume these might be more than the '76 450SL's 55 Watt jobbie.

Problem with the stock alternator is that a modern radio with a high watt amp in the trunk taxes the alternator and regulator beyond its limits.

A couple weeks ago my alt/reg fried and my alt was pumping almost 17 volts into the battery. Needless to say it fried the battery. I bought one alternator at the yard and it lasted 1 week. Luckily I bought the warranty. I see the same connector and bolt config in many models - even newer ones suuprisingly. I'll let you know what I find.

Rob