Unless they have changed recently, you are going to find that the king springs for datto 1200s are NOT captive at full suspension droop. So you'd need to address that. What's just as bad, imo, is that they are barely noticeable as far as being stiffer than stock ones.

AFter having issues with the std kings low spec, I ended up talking with them, and used the springs normally for the rear of a hyundai excel. They have a higher rate, but then the car sat higher than stock. to get it back to stock ride height I cut *(carefully of course, and a bit at a time, cooling in water between cuts) approx 1 full coil off them. That means they are just barely captive (but safe) with a stock ride height, nd have a slightly better spring rate.
they are part number khrl-115 from memory. I only used them as I got them as a swap when I handed the other ones back in and discussed the issue. But they are still way too soft - even for a stock a-b car they are still too soft imo.

SO I'm going with cut down gemini springs (of the people who have used them, I think most go for the variable rate ones, but I went with linear rate ones off the earlier geminis (TX?? I can look it up if you need me to). They have about the stiffest rate you'd want (they start off thicker material, but then you also need to cut them a bit to get the ride height down to std or lower if that's what you want) for a streeter and probably ok for some fun level competitions/runs. The only issue with them is they are way too short to be captive at full suspension droop. The trick there is to swap in different strut inserts/shocks. It's in the wiki pages, but basically there are a couple of options from other cars which fit into the strut, but are shorter so the spring will once again be captive.

I think I might have a pair of the king springs to suit the 1200s - they were in the rolled rally car that Andy originally bought a while back). I am so dead set serious about them being a bad choice, I'm willing to give them to anyone for the purpse of trying them just to confirm their suitability (or lack thereof) so nobody else drops money on them.

I'll double check if I can read the part numbers on the springs in question. They might be std ride height ones seeing that it was on a rally car, but even then they'll still be 95% as bad as the low ones (goodness only knows if there are superlows, and how bad they might be for them)