Sas is code for solid axle swap, it means removing all th independent front suspension and replacing it with a solid beam axle, like the first surfs had and all the early hiluxes had. Makes truck mental good offroad! Yes it's a big job and it's expensive,( possibly up to five grand depending how you go about it)
The good news is: if you're just doing towing and a bit of offroading that's not too hardcore then sassing your surf is totally unnecessary, standard ones are fine so long as you don't start acting like a total animal

.... Then it's sas time. Go to YouTube and type in sas 4runner!