I have now added the Bennie van der Walt pages to All of life redeemed.
There are two of his papers online:
1983. The consistent problem-historical method of philosophical historiography. Anakainosis 5 (2 and 3): 1-23 [pdf]
2000. 'Culture, worldview and religion' Cultures and Christianity AD 2000: International Symposium of the Association for Reformational Philosophy Aug 2000. [pdf]