I think it should widely acknowledged the genius of Barry Richards & Mike Procter (obviously G.Pollock) with Lee Irvine not to be forgotten who pretty much only played single figures in games like them from the same time.
Eddie Barlow, Trevor Goddard, Graeme Pollock, Colin Bland, Denis Lindsay, Peter Pollock all played a decent amount of test matches who started early 60s and a little before for Goddard to have it in numbers who were still around in those last 2 series wins over Australia. Obviously some would have carried on for a while yet.
Those with minimal games or none (leaving out those playing for other countries like D' Oliveira, Greig, Lamb, Wessles)
On Richards and Procter level I suppose you could make cases for Peter Kirsten, Clive Rice , Vince Van der Bijl, Garth Le Roux but probably in Cat B with Lee Irvine but some could easily argue their point.
The level below the above in Cat C but still very very high you looking at Jimmy Cook , Ken McEwan , Alan Kourie, Denys Hobson, Rupert Hanley, Kenny Watson
Cat D : Henry Fotheringham , Hylton Ackerman, Kevin McKenzie, Ray Jennings, Stephen Jefferies