The Buccaneers were definitely not in it for the long haul. Too few, ageing airframes.
There was mention of an avionics upgrade, using the Cheetah C radar, to keep the small fleet viable as a "silver bullet" until Carver arrived.
On Carver, as explained, the move to a larger twin engined configuration was driven by a long range strike capability.
And I suspect nuclear delivery was an important part of that.
It was stated it had to be a multi-role platform replacing not only the Mirage and Cheetah fighters, but also the Buccaneers and Canberra's.
I'm not sure anyone knows whether the TEL vehicle was based on the G-6 or Beestrok.
It was an 8x8, and those were 6x6.
The TEL vehicles, developed at the "Spes B" facility, are one of the great and enduring mysteries...both their design, and what happened to them eventually.
From what has been garnered, the MRBM (RSA 1, 2, and 3) force was to be both mobile (TEL) and silo based.
I suspect the silo based would have been initially the MRBM, but centered eventually on the ICBM (RSA-4).
South Africa is a large country (roughly in the ballpark area size of France, Germany, and Spain combined) so a mobile force was I think a given.