I don’t think you can convert them. The original Flight Simulator didn’t use a 3D global coordinate system (in fact the scenery wasn’t even on a globe - just a 2D plane). The coordinates from the early days were just a grid overlaid on a 2D map. From memory the coordinates ranged from -32767 to +32767 in both the X and Y grid.
They used “North” and “East” as a general term in the simulator, but I don’t think it really equated to hemispheres. From the Commodore 64 manual, it reads that each unit is approximately 256 metres so there is no convergence if you go further north - it is a fixed distance.
It was just a limitation of the technology and memory requirements of the day when the early versions of Flight Simulator came out. We finally moved to a 3D globe with Lat and Long with FS5 in 1993.