Remember due to S13 suspension setup, you make the front LCA to suit the Hub not the coilover, as the coilover doesn't connect to the LCA.
That's one of 2 ways u can do it, or you weld the bottom of the coilover the spindle hub.
What Silent Shadow i think is trying to say is, use the standard rear strut tops and put them on the coilover. In my experience this did not work with my HSD coilovers.
I run 8 & 6kg spring rates in my car, and coming from standard springs, yes it is harsher but is a huge upgrade on cornering.