Good tires (you can fit 33x10.50x15's on there with minimal or no rubbing) and good driving will get you a long way. The 2nd gen 4runner is a pretty capable offroad vehicle right out of the box - good ground clearance, short wheelbase, narrow, good low gears.
That being said, the 2nd gen IFS doesn't have a lot of travel, so my biggest problem was deep diagonal water breaks across an uphill stretch of trail. The suspension would get crossed up, a wheel on opposite corners would lift, and I would stop moving.
I solved that by putting the Aussie locker in the front. Completely eliminates that issue, and the truck will pretty much go anywhere now. I think a locker is a better solution than the SAS, plus it's an easier mod. The SAS will reduce the wheel lift problem, but won't eliminate it. The locker will make wheel lift irrelevant.
But, I too would first encourage you to run the truck as is and explore its limitations based on your needs. It may well do everything you want.