Dutch and Afrikaans differ slightly in pronunciation and spelling, and much more in popular perceptions. In Afrikaans I'd expect either Lodewyk or Lood; sometimes Loods as an echo of Lodevicus. Matthys is common; Martiens (echoing Marthinus, which is also used and shortens to Thinus) is more usual than Martyn (which I've never seen). Baltasar or Balthasar and Josef are used. The letter z doesn't exist in Afrikaans except in loan words or if people get creative with girl names: think Zola Budd.
Gert is used rather than Geert; also Gerhard, Gerard and Gerrit. Konrad and Coenraad both appear; Jakobus or Jacobus can shorten to Jacob, Jakob, Kobus, Koos, Jaco and Jaap.
What sort of references have you got in mind? To my knowledge there isn't a scholarly study of Afrikaans given names that's readily available, though there may well be some. The baby name books are ... not scholarly!
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