First of all I would suggest you are wasting your time with a K motor unless it is a really serious build.
Second, any cooler matrix made for an S13 will be way to big for a K series. If you do fit one, would be critically important to fit a thermostat otherwise the oil will always be too cold, which is very bad.
Seriously, it is a waste of time.
If you are still really keen, go here and download the catalogue which has a lot of relevant info about how, why and design issues for your system. Plus every part you can imagine.