Peter Pig's 'Professionals' and Vietnam Australians are perfect for the SADF of the 1970s and early 80s; before the R4 (Galil copy) was introduced (but don't use the Vietnam M60 GPMGs). They're also perfect for the SWATF (native Namibian) battalions, who continued to be armed with the R1 (FN FAL) or the G3, which is similar enough in 15mm.
The SADF did issue a plastic helmet in the 80s, which made them look near-identical to Israelis. However, it was very rarely worn (if at all) in the heat of Namibia and Angola.
Peter Pig do sell separate heads, so your best bet for late 80s SADF troops is to buy their Israelis and swap heads. I freely confess however, to simply using the Peter Pig Israelis with helmets – they still look the part.
For 32 Battalion and Recce-Commandos (as well as the FAPLA opposition), your best bet is the Peter Pig 'Hardened Militia' in cap, with Soviet weapons. However, 32 Battalion changed to regular SADF uniforms and kit when used in a conventional mechanised role from 1987 onward.
The links are blocked from my work computer here, but have a google for Johan Schoeman's excellent 'War in Angola in Miniature' webpage. There are also some scenarios, orbats and photos of my kit at fireandfury.com
snapped some photos of games he didn't get a chance to play in at Council of Five Nations.