K shocks aren't to bad I think its the cheaper version of k Sport. Boss has k Sport in his vl and I've had k Sport in a 31 before and not much worse quality then bc. (Not really bragging about k shock quality its just bc isnt the best but it's definitely the lowest of the spectrum id bother fitting to the car)
The Spring rates will be stiffer then king springs a lot stiffer. They're probably 8kg front 6kg rears. It all depends on what you want the car to drive like and profile of tyres. But should be 16-32 way dampening adjustable which will make a huge difference in the ride harshness.
My 4 cylinder Silvia has 10kg front springs 8kg rear and isnt to bad you could probably call heads or tails Rolling over a coin lol. My Skyline has the same rates but running the 6 cylinder up front I find it a little more forgiving. In saying that though almost all my cars you push down on and the tyre flexes and nothing more lol.
King springs are renowned at being over soft and one of the reasons commodores with suspension mods don't handle. The sl in rear will probably sit slightly higher then the front. You definitely want the hd as the rates slightly higher and will kill some of the squat and Mexican wave tip in effect.
Monroe gt aren't to bad value for money they're slightly stiffer then stock and apparently valved to king Spring Spring rates ( soft af lol) . If you want it stiffer Lovells are much better handling wise then king but compared to 115 a pair trade they're about $200. Or you can run Ute hd towing springs that's the next step for me in my senator before custom ive tried 4 rear pairs now lol.