This car isn't a conversion, there is no schraeder valve. Its like a little pyramid inside the fitting. I took the high side off thinking the car was an R12 car because I do replace the schraeders and fittings when I service conversion cars. The high side fitting had a big spring in it, and if you look straight into it its the same domed surface, not a schraeder.

This is an original R134a Mercedes fitting

I'll try to take a picture.