hello and welcome
check out the project cars section for the silvia front end conversion
the quick response would be that no silvia bodykit will fit without extensive modification. s13 has completely different guard setups, s14 is an entirely different shape and s15 requires hella amount of modification.
As for the rear bar, well the exhaust is on the wrong side, and the rear quarter panels are set up differently too. so its more or less a no go zone too.