How to tell if AC has been converted

[Oliver]

Hi all,
In the process of getting all of the systems in my '80 300sd functional, the AC seems like one of the more complicated. I know a lot of old cars have been converted to r134 and I've been having a hard time finding any definitive information on how one can tell if their car has been converted. I'll attach a couple of pictures of some fittings and things on my car's AC and I'm hoping someone can tell me if they look original or if it's been converted.


If these pictures don't really show anything I can take some more.
Oh and I also heard that computer duster can be used to refill non-concerted r12 systems, has anyone tried this on an old Benz?

Thanks