I had a TypeG that I'm sure I posted here on NE.
The G is quite similar to the African model. The only way I for sure knew mine was a G is that it was stamped in the barrel channel with a 'G' preceding the serial number matching the action.
Gs having a little schnabel in the forend where African models were smooth out to the end. Not 100% sure though.
If your barrel is 20", I agree that it probably is a TypeS with a shortened stock.