How direct fit are S13 rear coilovers

Hoping this isnt a stupid question but recently been doing quite a bit of thinking regarding the suspension of my z31, as Id like to get some fitment points. As much as powertrixx tempts me, im trying to figure out something cheaper, as I dont care much for ride quality and wont be tracking it anytime soon. I have access to some nice new front lowering springs, and have a few friends with spare coilovers for their s13s. Essentially my question is, how bolt on are s13 rear coilovers, and would it be bad to run them with lowering springs on the front. In Australia so cant really go too low anyway.