There is a repair
kit for your alternator
They may be able to tell you more.
The manufacturer website does not list it anymore, as you likely know, but they have a few tech support numbers. Try them and see if they have any info on it. It has got to be a retrofit item, I've never heard of that brand and it is not what is on our 1985 C30 with an M-25.
I can't imagine someone would replace a 55 amp alt for a 4. Maybe it is just 'code' for 55?