Converting RGB composite output to VGA
As Cheibriados has pointed out , E stands for Earth, and S stands for Sync.

Most likely, a video game used simple 1-bit encoding for the RGB levels, and if so that will make your life simpler. You'll need to get the use of a scope to look at the outputs, making sure to reference the scope to earth. With luck, you'll see essentially binary levels, although the actual levels may be somewhat high. If so, you can simply put 3 comparators on the RGB lines, and buffer the outputs so that they drive 75 ohms from 0 to 0.7 volts. This will drive VGA properly. If the color lines show a wide range of values, you'll need to get some op amps with relatively high speed (~5 MHz or better at operating gain - not gain-bandwidth) and buffer the signals to a range of 0 to 0.7 volts into 75 ohms. There may or may not be a sign inversion, and you may need to adjust offsets.

A single sync line establishes the use of composite sync, which means you'll need to provide a sync separator. South Africa uses PAL, so you'll need a unit which works in this format (I'm US, so I have no pertinent experience). The separator will produce separate horizontal and vertical syncs which are sent to the monitor. Signal levels are TTL, not 0 - 0.7 volts. I expect that any modern monitor will have no trouble handling PAL format syncs, but it's barely possible that you'll have to do some modification of the both pulse width and position wrt the video data.