3 the 3 link is part of a sway bar system and putting a 4 link on a truck that came with a 3 link will require a bigger sway bar because there will be more body roll. I dont know why.

Del Sphere Pivot Joints Roto Joint
3 link suspension vs 4 link. Theres no better method to setting the roll center height and keeping an axle laterally constrained than a track bar period. I researched a full year on pirate4x4 prior to tackling my rear 4 link suspension on my fj40. Even the heims are all still original. 4 an item that may not be a large factor but still should be considered is at full suspension droop. 3 link rears are very cool and if executed correctly will perform even better than a triangulated 4 link. He didnt say triangulated 4 link but did say he was looking for lateral control so im assuming he was thinking parallel bar 4 link.
I still run the 3 link on my mostly stock scx10 with no problems but on my dual motor rig the 3 link just had way to much movement. The articulation will also be smoother with the 4 link. A 3 link will be fine just gotta make sure its really stout for the upper link and mounts. And do some reading about the geometry for them. All too often track bars are made out to be an enemy and thats just not the case. And to get that you need some tall brackets.
They are simple to a fault. It got one minor adjustment but has largely worked. You will also get axle twisting more with the 3 link. And as far as the parallel 4 link goes yer right they have been mostly geared towards the drag cars or pro street trucks and cars. The 3 link setups will have more side to side axle movement than the 4 link setup. A 4 link suspension is geared for adjustability.
Poor front or rear geometry on a link suspension will make cornering exciting and emergency handling downright dangerous. Most guys dont need that much adjustability.