First thing you can do is to look at the rough list that I've been keeping here on the forum. Click on Knowledge Base then BMW Model Info. Find the R50 or type in your VIN at the top of the page. At the bottom of that page is a PDF that shows these sort of things that I've gleaned over the years. It's not perfect but it's a start.
As far as specific info for your bike, you would need to email BMW Archives and provide them what you have on the bike and they will do research and hopefully get back to you with some details. Here are a few emails to choose from...either one of them should get to them:
'78 R100/7 '69 R69S '52 R25/2
the email address firstname.lastname@example.org was rejected for whatever reason