Well, mainly unique in the muzzle attachments and the sheet steel handguards. The StG-58 also uses a buttstock with a straighter comb on it like a HK G3 stock has.
The standard Belgian 50.00 model was used all over the world and built by Brazil, Argentina, Chile, South Africa........
The 50.00 model has the Belgian short flash suppressor/grenade launcher/muzzle brake/bayo attachment device, and typically has black synthetic stock sets although wood stocks would also be "correct".
Couple of pics from Rhodesia/Zimbabwe of cammo'd 50.00 FAL's.
Here's an excellent article by Kokalis that's about 23 years old but still valid.